Merge -c 1584954 from trunk to branch-2 to fix YARN-1898. Addendum patch to ensure /jmx and /metrics are re-directed to Active RM.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1584955 13f79535-47bb-0310-9956-ffa450edef68