[SPARK-20487][SQL] `HiveTableScan` node is quite verbose in explained plan

## What changes were proposed in this pull request?

Changed `TreeNode.argString` to handle `CatalogTable` separately (otherwise it would call the default `toString` on the `CatalogTable`)

## How was this patch tested?

- Expanded scope of existing unit test to ensure that verbose information is not present
- Manual testing

Before

```
scala> hc.sql(" SELECT * FROM my_table WHERE name = 'foo' ").explain(true)
== Parsed Logical Plan ==
'Project [*]
+- 'Filter ('name = foo)
   +- 'UnresolvedRelation `my_table`

== Analyzed Logical Plan ==
user_id: bigint, name: string, ds: string
Project [user_id#13L, name#14, ds#15]
+- Filter (name#14 = foo)
   +- SubqueryAlias my_table
      +- CatalogRelation CatalogTable(
Database: default
Table: my_table
Owner: tejasp
Created: Fri Apr 14 17:05:50 PDT 2017
Last Access: Wed Dec 31 16:00:00 PST 1969
Type: MANAGED
Provider: hive
Properties: [serialization.format=1]
Statistics: 9223372036854775807 bytes
Location: file:/tmp/warehouse/my_table
Serde Library: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
InputFormat: org.apache.hadoop.mapred.TextInputFormat
OutputFormat: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
Partition Provider: Catalog
Partition Columns: [`ds`]
Schema: root
-- user_id: long (nullable = true)
-- name: string (nullable = true)
-- ds: string (nullable = true)
), [user_id#13L, name#14], [ds#15]

== Optimized Logical Plan ==
Filter (isnotnull(name#14) && (name#14 = foo))
+- CatalogRelation CatalogTable(
Database: default
Table: my_table
Owner: tejasp
Created: Fri Apr 14 17:05:50 PDT 2017
Last Access: Wed Dec 31 16:00:00 PST 1969
Type: MANAGED
Provider: hive
Properties: [serialization.format=1]
Statistics: 9223372036854775807 bytes
Location: file:/tmp/warehouse/my_table
Serde Library: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
InputFormat: org.apache.hadoop.mapred.TextInputFormat
OutputFormat: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
Partition Provider: Catalog
Partition Columns: [`ds`]
Schema: root
-- user_id: long (nullable = true)
-- name: string (nullable = true)
-- ds: string (nullable = true)
), [user_id#13L, name#14], [ds#15]

== Physical Plan ==
*Filter (isnotnull(name#14) && (name#14 = foo))
+- HiveTableScan [user_id#13L, name#14, ds#15], CatalogRelation CatalogTable(
Database: default
Table: my_table
Owner: tejasp
Created: Fri Apr 14 17:05:50 PDT 2017
Last Access: Wed Dec 31 16:00:00 PST 1969
Type: MANAGED
Provider: hive
Properties: [serialization.format=1]
Statistics: 9223372036854775807 bytes
Location: file:/tmp/warehouse/my_table
Serde Library: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
InputFormat: org.apache.hadoop.mapred.TextInputFormat
OutputFormat: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
Partition Provider: Catalog
Partition Columns: [`ds`]
Schema: root
-- user_id: long (nullable = true)
-- name: string (nullable = true)
-- ds: string (nullable = true)
), [user_id#13L, name#14], [ds#15]
```

After

```
scala> hc.sql(" SELECT * FROM my_table WHERE name = 'foo' ").explain(true)
== Parsed Logical Plan ==
'Project [*]
+- 'Filter ('name = foo)
   +- 'UnresolvedRelation `my_table`

== Analyzed Logical Plan ==
user_id: bigint, name: string, ds: string
Project [user_id#13L, name#14, ds#15]
+- Filter (name#14 = foo)
   +- SubqueryAlias my_table
      +- CatalogRelation `default`.`my_table`, [user_id#13L, name#14], [ds#15]

== Optimized Logical Plan ==
Filter (isnotnull(name#14) && (name#14 = foo))
+- CatalogRelation `default`.`my_table`, [user_id#13L, name#14], [ds#15]

== Physical Plan ==
*Filter (isnotnull(name#14) && (name#14 = foo))
+- HiveTableScan [user_id#13L, name#14, ds#15], CatalogRelation `default`.`my_table`, [user_id#13L, name#14], [ds#15]
```

Author: Tejas Patil <tejasp@fb.com>

Closes #17780 from tejasapatil/SPARK-20487_verbose_plan.