HDFS-4877. Merging change r1490421 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490430 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4867. metaSave NPEs when there are invalid blocks in repl queue. Contributed by Plamen Jeliazkov and Ravi Prakash.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490434 13f79535-47bb-0310-9956-ffa450edef68
Merge r1490437 from trunk to branch-2 for YARN-761. TestNMClientAsync fails sometimes (Zhijie Shen via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1490440 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-MAPREDUCE-4884-branch-2-gd