@Override
      protected void chore() {
        cleanUpOldNonces();
      }
Creates a scheduled chore that is used to clean up old nonces.
@param stoppable Stoppable for the chore.
@return ScheduledChore; the scheduled chore is not started.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ServerNonceManager.java