YARN-1706. Created an utility method to dump timeline records to JSON strings. Contributed by Zhijie Shen.
svn merge --ignore-ancestry -c 1566982 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1566983 13f79535-47bb-0310-9956-ffa450edef68