svn merge -c 1569368. merging from trunk to branch-2 to fix:HDFS-5780. TestRBWBlockInvalidation times out intemittently.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1569468 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1569391 merging from trunk to branch-2 to fix:HDFS-5803. TestBalancer.testBalancer0 fails.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1569469 13f79535-47bb-0310-9956-ffa450edef68