HDFS-4685. Merge HDFS ACLs to branch-2.  Merging changes r1569870, r1570466, r1570655, r1571573, r1571745, r1572142, r1572189 and r1572190 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1572308 13f79535-47bb-0310-9956-ffa450edef68