YARN-1667. Modified RM HA handling of super users (with proxying ability) to be available across RM failover by making using of a remote configuration-provider. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1564100 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1564101 13f79535-47bb-0310-9956-ffa450edef68