On Master@shutdown, close the shared Master connection to kill any
ongoing RPCs by hosted clients.
M hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java
Call close ont the Master shared clusterconnection to kill any ongoing
rpcs.
M hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java
Remove guts of close; we were closing the Masters connection....not
our responsibility.
Added unit test written by Duo Zhang which demonstrates the case where
Master will not go down.
Signed-off-by: zhangduo <zhangduo@apache.org>