YARN-590. Added an optional mesage to be returned by ResourceMaanger when RM asks an RM to shutdown/resync etc so that NMs can log this message locally for better debuggability. Contributed by Mayank Bansal.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1481234 13f79535-47bb-0310-9956-ffa450edef68