HDFS-4632. Merging change r1514168 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1514169 13f79535-47bb-0310-9956-ffa450edef68
merge YARN-1045. Improve toString implementation for PBImpls. Contributed by Jian He.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1514186 13f79535-47bb-0310-9956-ffa450edef68