YARN-1659. Defined the ApplicationTimelineStore store as an abstraction for implementing different storage impls for storing timeline information. Contributed by Billie Rinaldi.
svn merge --ignore-ancestry -c 1564037 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1564038 13f79535-47bb-0310-9956-ffa450edef68