YARN-1696. Added documentation for ResourceManager fail-over. Contributed by Karthik Kambatla, Masatake Iwasaki, Tsuyoshi OZAWA.
svn merge --ignore-ancestry -c 1591416 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1591417 13f79535-47bb-0310-9956-ffa450edef68