YARN-1658. Modified web-app framework to let standby RMs redirect web-service calls to the active RM. Contributed by Cindy Li.
svn merge --ignore-ancestry -c 1577408 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1577410 13f79535-47bb-0310-9956-ffa450edef68