YARN-1637. Implemented a client library for Java users to post timeline entities and events. Contributed by Zhijie Shen.
svn merge --ignore-ancestry -c 1566752 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1566753 13f79535-47bb-0310-9956-ffa450edef68