[SPARK-17698][SQL] Join predicates should not contain filter clauses

## What changes were proposed in this pull request?

Jira : https://issues.apache.org/jira/browse/SPARK-17698

`ExtractEquiJoinKeys` is incorrectly using filter predicates as the join condition for joins. `canEvaluate` [0] tries to see if the an `Expression` can be evaluated using output of a given `Plan`. In case of filter predicates (eg. `a.id='1'`), the `Expression` passed for the right hand side (ie. '1' ) is a `Literal` which does not have any attribute references. Thus `expr.references` is an empty set which theoretically is a subset of any set. This leads to `canEvaluate` returning `true` and `a.id='1'` is treated as a join predicate. While this does not lead to incorrect results but in case of bucketed + sorted tables, we might miss out on avoiding un-necessary shuffle + sort. See example below:

[0] : https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala#L91

eg.

```
val df = (1 until 10).toDF("id").coalesce(1)
hc.sql("DROP TABLE IF EXISTS table1").collect
df.write.bucketBy(8, "id").sortBy("id").saveAsTable("table1")
hc.sql("DROP TABLE IF EXISTS table2").collect
df.write.bucketBy(8, "id").sortBy("id").saveAsTable("table2")

sqlContext.sql("""
  SELECT a.id, b.id
  FROM table1 a
  FULL OUTER JOIN table2 b
  ON a.id = b.id AND a.id='1' AND b.id='1'
""").explain(true)
```

BEFORE: This is doing shuffle + sort over table scan outputs which is not needed as both tables are bucketed and sorted on the same columns and have same number of buckets. This should be a single stage job.

```
SortMergeJoin [id#38, cast(id#38 as double), 1.0], [id#39, 1.0, cast(id#39 as double)], FullOuter
:- *Sort [id#38 ASC NULLS FIRST, cast(id#38 as double) ASC NULLS FIRST, 1.0 ASC NULLS FIRST], false, 0
:  +- Exchange hashpartitioning(id#38, cast(id#38 as double), 1.0, 200)
:     +- *FileScan parquet default.table1[id#38] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table1, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
+- *Sort [id#39 ASC NULLS FIRST, 1.0 ASC NULLS FIRST, cast(id#39 as double) ASC NULLS FIRST], false, 0
   +- Exchange hashpartitioning(id#39, 1.0, cast(id#39 as double), 200)
      +- *FileScan parquet default.table2[id#39] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table2, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
```

AFTER :

```
SortMergeJoin [id#32], [id#33], FullOuter, ((cast(id#32 as double) = 1.0) && (cast(id#33 as double) = 1.0))
:- *FileScan parquet default.table1[id#32] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table1, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
+- *FileScan parquet default.table2[id#33] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table2, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
```

## How was this patch tested?

- Added a new test case for this scenario : `SPARK-17698 Join predicates should not contain filter clauses`
- Ran all the tests in `BucketedReadSuite`

Author: Tejas Patil <tejasp@fb.com>

Closes #15272 from tejasapatil/SPARK-17698_join_predicate_filter_clause.