HDFS-4632. Merging change r1514169 from branch-2 to branch-2.1-beta.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1514170 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-2.1-beta@1514187 13f79535-47bb-0310-9956-ffa450edef68