HDFS-5077. NPE in FSNamesystem.commitBlockSynchronization().  Contributed by Plamen Jeliazkov.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1518854 13f79535-47bb-0310-9956-ffa450edef68
YARN-707. Added user information also in the YARN ClientToken so that AMs can implement authorization based on incoming users. Contributed by Jason Lowe.
svn merge --ignore-ancestry -c 1518868 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1518870 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9774. Merging change r1518865 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1518876 13f79535-47bb-0310-9956-ffa450edef68