HDFS-6173. Merge r1583384 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583385 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10451. Merge r1583393 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583395 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10345. Merge change r1583454 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583457 13f79535-47bb-0310-9956-ffa450edef68