Fix CME in ReplicationSourceManager

Exception in thread "regionserver/hostname/ip:port" java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
        at java.util.ArrayList$Itr.next(ArrayList.java:851)
        at org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceManager.join(ReplicationSourceManager.java:832)
        at org.apache.hadoop.hbase.replication.regionserver.Replication.join(Replication.java:162)
        at org.apache.hadoop.hbase.replication.regionserver.Replication.stopReplicationService(Replication.java:155)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.stopServiceThreads(HRegionServer.java:2623)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:1175)
        at java.lang.Thread.run(Thread.java:745)