Merge r1523750 from trunk to branch-2 for YARN-1027. Implement RMHAProtocolService (Karthik Kambatla via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1523753 13f79535-47bb-0310-9956-ffa450edef68