svn merge -c 1577647 FIXES: MAPREDUCE-5769. Unregistration to RM should not be called if AM is crashed before registering with RM. Contributed by Rohith


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1577649 13f79535-47bb-0310-9956-ffa450edef68