Added some new tests

[TheRealHaui]

Added some new tests to increase test code coverage.

[lizhimins]

It is recommended to merge them into one; avoid using AI to generate low-quality use cases.

[TheRealHaui]

@lizhimins,
if you want I can of course merge all the individual tests I added for the individual methods - CommandUtil.fetchBrokerNameByAddr, ...fetchMasterAndSlaveAddrByBrokerName, ...fetchMasterAddrByBrokerName and ...fetchMasterAndSlaveAddrByClusterName - into one big test method.
Most organizsations however prefer individual Unit Tests for their individual methods/units of code.
Further, this pattern is used in the code base for all pre-existing Unit Tests of the CommandUtil class too.
Aside of other already existing Unit Tests - e.g. in the DefaultMonitorListenerTest class.

The Unit Tests were not generated by any whatsoever AI!