YARN-1321. Changed NMTokenCache to support both singleton and an instance usage. Contributed by Alejandro Abdelnur.
svn merge --ignore-ancestry -c 1537334 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1537335 13f79535-47bb-0310-9956-ffa450edef68