[Test] Unit tests Zookeeper client always print Connection refused exception when connecting to the Zookeeper server

[hangc0276]

Description

When I run BookKeeper unit tests, such as BookieDecommissionTest#testDecommissionBookie, the zookeeper client always print the following exceptions when connecting to the Zookeeper server.

2023-02-27T17:59:09,010 - WARN  - [Time-limited test-SendThread(localhost:59156):ClientCnxn$SendThread@1300] - Session 0x0 for server localhost/0:0:0:0:0:0:0:1:59156, Closing socket connection. Attempting reconnect except it is a SessionExpiredException.
java.net.ConnectException: Connection refused
	at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[?:1.8.0_131]
	at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717) ~[?:1.8.0_131]
	at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:344) ~[zookeeper-3.8.1.jar:3.8.1]
	at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1289) ~[zookeeper-3.8.1.jar:3.8.1]

I'm not sure whether it is the expected behavior.