YARN-925. Defined a Reader Interface for HistoryStorage. Contributed by Mayank Bansal.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/YARN-321@1508228 13f79535-47bb-0310-9956-ffa450edef68
YARN-978. Created ApplicationAttemptReport. Contributed by Mayank Bansal.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/YARN-321@1508614 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch 'apache/YARN-321' into YARN-953
Address vinod's comments