HDFS-4372. Merging change r1502120 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1502419 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4373. Merging change r1502328 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1502423 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4374. Merging change r1502331 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1502426 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-YAHOO-286-branch-2-gd