Merge from trunk HIVE-7878 - add -- SORT_BEFORE_DIFF to optimize_nullscan.q test (Venki Korukanti reviewed by Szehon)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1620671 13f79535-47bb-0310-9956-ffa450edef68