Enhance test case TestEtctlutlMigrate to support multiple member cluster

[ahrtr]

This PR is extracted from #19168

cc @fuweid @serathius @ivanvc @jmhbnz @siyuanfoundation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.73%. Comparing base (9db8dcb) to head (c2025cb).
Report is 13 commits behind head on main.

Additional details and impacted files

see 25 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19174      +/-   ##
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- Coverage   68.87%   68.73%   -0.15%     
==========================================
  Files         420      420              
  Lines       35649    35649              
==========================================
- Hits        24554    24503      -51     
- Misses       9674     9718      +44     
- Partials     1421     1428       +7     

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[serathius]

What's the benefit of running command on 3 member cluster if we just run it 3 times and never start the cluster?

[ahrtr]

What's the benefit of running command on 3 member cluster if we just run it 3 times and never start the cluster?

It will be useful to the following PR. It's just to make reviewing the following PR easier.

I will try to start the members again after the migrating. For example, after we migrate from 3.6 to 3.5, we should be able to start the members with 3.5 binary.

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