HIVE-7652 : Check OutputCollector after closing ExecMapper/ExecReducer (Venki Korukanti via Szehon) [Spark Branch]

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1616663 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'upstream/spark' into spark
Merge branch 'spark' into HIVE-7624