dubbo-cluster module change integration test to unit test

[CrazyHZM]

What is the purpose of the change?

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Make sure gitHub actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.55%. Comparing base (9e249cf) to head (3e04799).
Report is 3 commits behind head on 3.3.

Additional details and impacted files

@@           Coverage Diff           @@
##              3.3   #14929   +/-   ##
=======================================
  Coverage   37.55%   37.55%           
=======================================
  Files        1835     1835           
  Lines       81382    81382           
  Branches    12093    12093           
=======================================
+ Hits        30563    30566    +3     
- Misses      46377    46379    +2     
+ Partials     4442     4437    -5     

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