Merge r1609254 from trunk. YARN-1366. Changed AMRMClient to re-register with RM and send outstanding requests back to RM on work-preserving RM restart. Contributed by Rohith

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1609255 13f79535-47bb-0310-9956-ffa450edef68