Fix flaky test in cluster failover

[git-hulk]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.44%. Comparing base (6c56470) to head (b604bf4).
⚠️ Report is 88 commits behind head on unstable.

Files with missing lines	Patch %	Lines
store/cluster_node.go	0.00%	3 Missing ⚠️
controller/cluster.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #355      +/-   ##
============================================
+ Coverage     43.38%   47.44%   +4.05%     
============================================
  Files            37       45       +8     
  Lines          2971     4454    +1483     
============================================
+ Hits           1289     2113     +824     
- Misses         1544     2133     +589     
- Partials        138      208      +70     

Flag	Coverage Δ
unittests	47.44% <0.00%> (+4.05%)	⬆️

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[git-hulk]

It still has the flaky condition after the last fix. The root cause is that multiple test cases are sharing the same kvrocks cluster, and their migration status will affect each other. I have rerun it a few times, and it should be stable after this fix.

[git-hulk]

@PragmaTwice Thanks for your prompt review. Another issue to be improved is that cluster.Reset() should first flush the master node and then reset the other replicas. Or it may fail to reset replicas because some data is left inside the instance.