YARN-713. Fixed ResourceManager to not crash while building tokens when DNS issues happen transmittently. Contributed by Jian He.
svn merge --ignore-ancestry -c 1569979 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569980 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5868. Merging r1569978 from trunk to branch-2

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569982 13f79535-47bb-0310-9956-ffa450edef68