svn merge -c 1603571 from trunk for HDFS-6530. Fix Balancer documentation.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1603572 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6552: Merging r1603602 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1603603 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6551. Merge r1603612 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1603615 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6439. Merging change r1603622 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1603624 13f79535-47bb-0310-9956-ffa450edef68