YARN-1665. Simplify the configuration of RM HA by having better default values. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1565517 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1565518 13f79535-47bb-0310-9956-ffa450edef68