HIVE-4261 : union_remove_10 is failing on hadoop2 with assertion (root task with non-empty set of parents) (Gunther Hagleitner via Ashutosh Chauhan)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.11@1471629 13f79535-47bb-0310-9956-ffa450edef68