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@1569393 13f79535-47bb-0310-9956-ffa450edef68
YARN-1721. When moving app between queues in Fair Scheduler, grab lock on FSSchedulerApp (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569445 13f79535-47bb-0310-9956-ffa450edef68
YARN-1724. Race condition in Fair Scheduler when continuous scheduling is turned on (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569451 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5893. Merge change r1569477 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569478 13f79535-47bb-0310-9956-ffa450edef68