HIVE-8622: Split map-join plan into 2 SparkTasks in 3 stages [Spark Branch] (Chao via Xuefu)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1637855 13f79535-47bb-0310-9956-ffa450edef68
HIVE-8621: Dump small table join data for map-join [Spark Branch] (Jimmy via Xuefu)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1637860 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'upstream/spark' into spark
Merge remote branch 'origin/spark' into HIVE-8542