[SPARK-17612][SQL] Support `DESCRIBE table PARTITION` SQL syntax

## What changes were proposed in this pull request?

This PR implements `DESCRIBE table PARTITION` SQL Syntax again. It was supported until Spark 1.6.2, but was dropped since 2.0.0.

**Spark 1.6.2**
```scala
scala> sql("CREATE TABLE partitioned_table (a STRING, b INT) PARTITIONED BY (c STRING, d STRING)")
res1: org.apache.spark.sql.DataFrame = [result: string]

scala> sql("ALTER TABLE partitioned_table ADD PARTITION (c='Us', d=1)")
res2: org.apache.spark.sql.DataFrame = [result: string]

scala> sql("DESC partitioned_table PARTITION (c='Us', d=1)").show(false)
+----------------------------------------------------------------+
|result                                                          |
+----------------------------------------------------------------+
|a                      string                                   |
|b                      int                                      |
|c                      string                                   |
|d                      string                                   |
|                                                                |
|# Partition Information                                         |
|# col_name             data_type               comment          |
|                                                                |
|c                      string                                   |
|d                      string                                   |
+----------------------------------------------------------------+
```

**Spark 2.0**
- **Before**
```scala
scala> sql("CREATE TABLE partitioned_table (a STRING, b INT) PARTITIONED BY (c STRING, d STRING)")
res0: org.apache.spark.sql.DataFrame = []

scala> sql("ALTER TABLE partitioned_table ADD PARTITION (c='Us', d=1)")
res1: org.apache.spark.sql.DataFrame = []

scala> sql("DESC partitioned_table PARTITION (c='Us', d=1)").show(false)
org.apache.spark.sql.catalyst.parser.ParseException:
Unsupported SQL statement
```

- **After**
```scala
scala> sql("CREATE TABLE partitioned_table (a STRING, b INT) PARTITIONED BY (c STRING, d STRING)")
res0: org.apache.spark.sql.DataFrame = []

scala> sql("ALTER TABLE partitioned_table ADD PARTITION (c='Us', d=1)")
res1: org.apache.spark.sql.DataFrame = []

scala> sql("DESC partitioned_table PARTITION (c='Us', d=1)").show(false)
+-----------------------+---------+-------+
|col_name               |data_type|comment|
+-----------------------+---------+-------+
|a                      |string   |null   |
|b                      |int      |null   |
|c                      |string   |null   |
|d                      |string   |null   |
|# Partition Information|         |       |
|# col_name             |data_type|comment|
|c                      |string   |null   |
|d                      |string   |null   |
+-----------------------+---------+-------+

scala> sql("DESC EXTENDED partitioned_table PARTITION (c='Us', d=1)").show(100,false)
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------+-------+
|col_name                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |data_type|comment|
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------+-------+
|a                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |string   |null   |
|b                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |int      |null   |
|c                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |string   |null   |
|d                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |string   |null   |
|# Partition Information                                                                                                                                                                                                                                                                                                                                                                                                                                                            |         |       |
|# col_name                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |data_type|comment|
|c                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |string   |null   |
|d                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |string   |null   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |         |       |
|Detailed Partition Information CatalogPartition(
        Partition Values: [Us, 1]
        Storage(Location: file:/Users/dhyun/SPARK-17612-DESC-PARTITION/spark-warehouse/partitioned_table/c=Us/d=1, 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])
        Partition Parameters:{transient_lastDdlTime=1475001066})|         |       |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------+-------+

scala> sql("DESC FORMATTED partitioned_table PARTITION (c='Us', d=1)").show(100,false)
+--------------------------------+---------------------------------------------------------------------------------------+-------+
|col_name                        |data_type                                                                              |comment|
+--------------------------------+---------------------------------------------------------------------------------------+-------+
|a                               |string                                                                                 |null   |
|b                               |int                                                                                    |null   |
|c                               |string                                                                                 |null   |
|d                               |string                                                                                 |null   |
|# Partition Information         |                                                                                       |       |
|# col_name                      |data_type                                                                              |comment|
|c                               |string                                                                                 |null   |
|d                               |string                                                                                 |null   |
|                                |                                                                                       |       |
|# Detailed Partition Information|                                                                                       |       |
|Partition Value:                |[Us, 1]                                                                                |       |
|Database:                       |default                                                                                |       |
|Table:                          |partitioned_table                                                                      |       |
|Location:                       |file:/Users/dhyun/SPARK-17612-DESC-PARTITION/spark-warehouse/partitioned_table/c=Us/d=1|       |
|Partition Parameters:           |                                                                                       |       |
|  transient_lastDdlTime         |1475001066                                                                             |       |
|                                |                                                                                       |       |
|# 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                                                                                      |       |
+--------------------------------+---------------------------------------------------------------------------------------+-------+
```

## How was this patch tested?

Pass the Jenkins tests with a new testcase.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #15168 from dongjoon-hyun/SPARK-17612.