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-2.4@1569981 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5868. Merging r1569982 from branch-2 to branch-2.4.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1569983 13f79535-47bb-0310-9956-ffa450edef68