Merge r1553596 from trunk. Fixed yarn rmadmin command to print the correct usage info. Contributed by Akira AJISAKA.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1553597 13f79535-47bb-0310-9956-ffa450edef68
YARN-1523. Use StandbyException instead of RMNotYetReadyException (kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1553620 13f79535-47bb-0310-9956-ffa450edef68