YARN-1325. Modified RM HA configuration validation to also ensure that multiple RMs are configured. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1550524 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1550527 13f79535-47bb-0310-9956-ffa450edef68