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@1569369 13f79535-47bb-0310-9956-ffa450edef68