MAPREDUCE-5117. Changed MRClientProtocolPBClientImpl to be closeable and thus fix failures in renewal of HistoryServer's delegations tokens. Contributed by Siddharth Seth.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1463828 13f79535-47bb-0310-9956-ffa450edef68