HIVE-4315 : enable doAs in unsecure mode for hive server2, when MR job runs locally (Thejas Nair via Ashutosh Chauhan)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.11@1468440 13f79535-47bb-0310-9956-ffa450edef68