YARN-1028. Added FailoverProxyProvider capability to ResourceManager to help with RM failover. Contributed by Karthik Kambatla.
svn merge --ignore-ancestry -c 1551739 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1551740 13f79535-47bb-0310-9956-ffa450edef68