[SPARK-17530][SQL] Add Statistics into DESCRIBE FORMATTED

### What changes were proposed in this pull request?
Statistics is missing in the output of `DESCRIBE FORMATTED`. This PR is to add it. After the PR, the output will be like:
```
+----------------------------+----------------------------------------------------------------------------------------------------------------------+-------+
|col_name                    |data_type                                                                                                             |comment|
+----------------------------+----------------------------------------------------------------------------------------------------------------------+-------+
|key                         |string                                                                                                                |null   |
|value                       |string                                                                                                                |null   |
|                            |                                                                                                                      |       |
|# Detailed Table Information|                                                                                                                      |       |
|Database:                   |default                                                                                                               |       |
|Owner:                      |xiaoli                                                                                                                |       |
|Create Time:                |Tue Sep 13 14:36:57 PDT 2016                                                                                          |       |
|Last Access Time:           |Wed Dec 31 16:00:00 PST 1969                                                                                          |       |
|Location:                   |file:/private/var/folders/4b/sgmfldk15js406vk7lw5llzw0000gn/T/warehouse-9982e1db-df17-4376-a140-dbbee0203d83/texttable|       |
|Table Type:                 |MANAGED                                                                                                               |       |
|Statistics:                 |sizeInBytes=5812, rowCount=500, isBroadcastable=false                                                                 |       |
|Table Parameters:           |                                                                                                                      |       |
|  rawDataSize               |-1                                                                                                                    |       |
|  numFiles                  |1                                                                                                                     |       |
|  transient_lastDdlTime     |1473802620                                                                                                            |       |
|  totalSize                 |5812                                                                                                                  |       |
|  COLUMN_STATS_ACCURATE     |false                                                                                                                 |       |
|  numRows                   |-1                                                                                                                    |       |
|                            |                                                                                                                      |       |
|# Storage Information       |                                                                                                                      |       |
|SerDe Library:              |org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe                                                                    |       |
|InputFormat:                |org.apache.hadoop.mapred.TextInputFormat                                                                              |       |
|OutputFormat:               |org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat                                                            |       |
|Compressed:                 |No                                                                                                                    |       |
|Storage Desc Parameters:    |                                                                                                                      |       |
|  serialization.format      |1                                                                                                                     |       |
+----------------------------+----------------------------------------------------------------------------------------------------------------------+-------+
```

Also improve the output of statistics in `DESCRIBE EXTENDED` by removing duplicate `Statistics`. Below is the example after the PR:

```
+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------+
|col_name                    |data_type                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |comment|
+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------+
|key                         |string                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |null   |
|value                       |string                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |null   |
|                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |       |
|# Detailed Table Information|CatalogTable(
	Table: `default`.`texttable`
	Owner: xiaoli
	Created: Tue Sep 13 14:38:43 PDT 2016
	Last Access: Wed Dec 31 16:00:00 PST 1969
	Type: MANAGED
	Schema: [StructField(key,StringType,true), StructField(value,StringType,true)]
	Provider: hive
	Properties: [rawDataSize=-1, numFiles=1, transient_lastDdlTime=1473802726, totalSize=5812, COLUMN_STATS_ACCURATE=false, numRows=-1]
	Statistics: sizeInBytes=5812, rowCount=500, isBroadcastable=false
	Storage(Location: file:/private/var/folders/4b/sgmfldk15js406vk7lw5llzw0000gn/T/warehouse-8ea5c5a0-5680-4778-91cb-c6334cf8a708/texttable, InputFormat: org.apache.hadoop.mapred.TextInputFormat, OutputFormat: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat, Serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, Properties: [serialization.format=1]))|       |
+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------+
```

### How was this patch tested?
Manually tested.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #15083 from gatorsmile/descFormattedStats.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/interface.scala

@@ -191,7 +191,7 @@ case class CatalogTable(
         viewText.map("View: " + _).getOrElse(""),
         comment.map("Comment: " + _).getOrElse(""),
         if (properties.nonEmpty) s"Properties: $tableProperties" else "",
-        if (stats.isDefined) s"Statistics: ${stats.get}" else "",
+        if (stats.isDefined) s"Statistics: ${stats.get.simpleString}" else "",
         s"$storage")
 
     output.filter(_.nonEmpty).mkString("CatalogTable(\n\t", "\n\t", ")")

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/Statistics.scala

@@ -38,12 +38,13 @@ case class Statistics(
     sizeInBytes: BigInt,
     rowCount: Option[BigInt] = None,
     isBroadcastable: Boolean = false) {
-  override def toString: String = {
-    val output =
-      Seq(s"sizeInBytes=$sizeInBytes",
-        if (rowCount.isDefined) s"rowCount=${rowCount.get}" else "",
-        s"isBroadcastable=$isBroadcastable"
-      )
-    output.filter(_.nonEmpty).mkString("Statistics(", ", ", ")")
+  override def toString: String = "Statistics(" + simpleString + ")"
+
+  /** Readable string representation for the Statistics. */
+  def simpleString: String = {
+    Seq(s"sizeInBytes=$sizeInBytes",
+      if (rowCount.isDefined) s"rowCount=${rowCount.get}" else "",
+      s"isBroadcastable=$isBroadcastable"
+    ).filter(_.nonEmpty).mkString("", ", ", "")
   }
 }

sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala

@@ -468,6 +468,7 @@ case class DescribeTableCommand(table: TableIdentifier, isExtended: Boolean, isF
     append(buffer, "Last Access Time:", new Date(table.lastAccessTime).toString, "")
     append(buffer, "Location:", table.storage.locationUri.getOrElse(""), "")
     append(buffer, "Table Type:", table.tableType.name, "")
+    table.stats.foreach(s => append(buffer, "Statistics:", s.simpleString, ""))
 
     append(buffer, "Table Parameters:", "", "")
     table.properties.foreach { case (key, value) =>