HDFS-5144. Merge r1518895 from trunk

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HDFS-5140. Merge change r1518899 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1518902 13f79535-47bb-0310-9956-ffa450edef68
Fix CHANGES.txt to remove repeated sections for 2.3.0

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1518908 13f79535-47bb-0310-9956-ffa450edef68