Merge -c 1516361 from trunk to branch-2 to fix MAPREDUCE-5475. Ensure MRClientService verifies ACLs for users. Contributed by Jason Lowe.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1516362 13f79535-47bb-0310-9956-ffa450edef68