HDFS-5065. Merging change r1537319 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1537320 13f79535-47bb-0310-9956-ffa450edef68
YARN-1321. Changed NMTokenCache to support both singleton and an instance usage. Contributed by Alejandro Abdelnur.
svn merge --ignore-ancestry -c 1537334 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1537335 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4633. Merging change r1461846 and r1537345 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1537347 13f79535-47bb-0310-9956-ffa450edef68
YARN-1343. NodeManagers additions/restarts are not reported as node updates in AllocateResponse responses to AMs. (tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1537369 13f79535-47bb-0310-9956-ffa450edef68