YARN-1611. Introduced the concept of a configuration provider which can be used by ResourceManager to read configuration locally or from remote systems so as to help RM failover. Contributed by Xuan Gong.
svn merge -c 1564002 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1564003 13f79535-47bb-0310-9956-ffa450edef68