HADOOP-9476. Some test cases in TestUserGroupInformation fail if ran after testSetLoginUser. Contributed by Robert Parker.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1511140 13f79535-47bb-0310-9956-ffa450edef68
Update CHANGES.txt for HADOOP-9476

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Merge remote branch 'origin/branch-0.23' into branch-0.23-gd
Merge remote branch 'origin/branch-0.23-gd' into fb-YAHOO-260-branch-0.23-gd