svn merge -c 1584900 Merging from trunk to branch-2 to fix:HDFS-6159. TestBalancerWithNodeGroup.testBalancerWithNodeGroup fails if there is block missing after balancer success.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1584901 13f79535-47bb-0310-9956-ffa450edef68