Merge r1605263 from trunk. YARN-1365. Changed ApplicationMasterService to allow an app to re-register after RM restart. Contributed by Anubhav Dhoot

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1605264 13f79535-47bb-0310-9956-ffa450edef68