Merge r1606557 from trunk. YARN-2052. Embedded an epoch number in container id to ensure the uniqueness of container id after RM restarts. Contributed by Tsuyoshi OZAWA

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1606558 13f79535-47bb-0310-9956-ffa450edef68