Merge r1526072 from branch-2 to branch-2.1-beta for MAPREDUCE-5505. Clients should be notified job finished only after job successfully unregistered (Zhijie Shen via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1526074 13f79535-47bb-0310-9956-ffa450edef68