HDFS-6828. Merge r1616889 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1616890 13f79535-47bb-0310-9956-ffa450edef68
YARN-2212 ApplicationMaster needs to find a way to update the AMRMToken periodically. Contributed by Xuan Gong


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1616891 13f79535-47bb-0310-9956-ffa450edef68