YARN-1761. Modified RMAdmin CLI to check whether HA is enabled or not before it executes any of the HA admin related commands. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1574661 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1574663 13f79535-47bb-0310-9956-ffa450edef68