HIVE-15757: Allow EXISTS/NOT EXISTS correlated subquery with aggregates

[kasakrisz]

What changes were proposed in this pull request?

1. When transforming subquery AST to calcite plan check whether the subquery is a full aggregation: has aggregate functions without group by clause
2. When building subquery expression return true literal if subquery is a full aggregation having EXISTS operator instead of RexSubQuery

Why are the changes needed?

To support queries like:

SELECT t1.bigint_col
FROM alltypestiny t1
WHERE EXISTS
  (SELECT SUM(smallint_col) AS int_col
   FROM alltypestiny
   WHERE t1.date_string_col = string_col AND t1.timestamp_col = timestamp_col)
GROUP BY t1.bigint_col

Does this PR introduce any user-facing change?

Yes. Current Hive implementation throws exception when compiling queries like the example above. With this patch query compiles and runs.

How was this patch tested?

mvn test -Dtest.output.overwrite -DskipSparkTests -Dtest=TestMiniLlapLocalCliDriver -Dqfile=subquery_full_aggregate.q -pl itests/qtest -Pitests

[jcamachor]

I gave +1 based on the code but I have just seen there are some test failures. Please let me know when those are addressed and I can take a look again. Thanks