HADOOP-9574. Added new methods in AbstractDelegationTokenSecretManager for helping YARN ResourceManager to reuse code for RM restart. Contributed by Jian He.
svn merge --ignore-ancestry -c 1487692 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1487693 13f79535-47bb-0310-9956-ffa450edef68