Cleanup CHANGES.txt to have consistent formatting and match the descrtion with CHANGES.txt in trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1475780 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4053. Merging change r1399908 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1475848 13f79535-47bb-0310-9956-ffa450edef68