HIVE-7766 - Cleanup Reduce operator code [Spark Branch] (Rui Li via Brock)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618642 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7763 - Failed to qeury TABLESAMPLE on empty bucket table [Spark Branch] (Chengxiang via Brock)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618646 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7606 - Design SparkSession, SparkSessionManager [Spark Branch] (Venki Korukanti via Brock)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618702 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7528 - Support cluster by and distributed by [Spark Branch] (Rui Li via Brock)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618707 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7745 - NullPointerException when turn on hive.optimize.union.remove, hive.merge.mapfiles and hive.merge.mapredfiles [Spark Branch] (Na Yang via Brock)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618708 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7755 - Enable avro* tests [Spark Branch] (Brock reviewed by Szehon)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618756 13f79535-47bb-0310-9956-ffa450edef68
HIVE-7530 - Go thru the common code to find references to HIVE_EXECUCTION_ENGINE to make sure conditions works with Spark (Na Yang via Brock) [Spark Branch]

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1618769 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch 'upstream/spark' into spark