HDFS-5614: fix incorrect fsimage serialization of AclFeature for inodes that do not have an ACL.
HDFS-5614: fix ACL modification APIs to always read current ACL state
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-4685-WIP
Merge branch 'HDFS-4685' into HDFS-5614
Merge branch 'HDFS-4685' into HDFS-5849
Merge branch 'HDFS-4685' into HADOOP-10270
merge HDFS-5614 to HDFS-4685-WIP
Merge branch 'HDFS-5849' into HDFS-4685-WIP
Merge branch 'HADOOP-10270' into HDFS-4685-WIP