Merge -c 1529015 from trunk to branch-2 to fix YARN-890. Ensure CapacityScheduler doesn't round-up metric for available resources. Contributed by Xuan Gong & Hitesh Shah.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1529018 13f79535-47bb-0310-9956-ffa450edef68