HDFS-5608. WebHDFS: implement ACL APIs. Contributed by Sachin Jose and Renil Joseph.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4685@1563013 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'HDFS-4685' into HDFS-5849