[store] test 3 candidates cluster

[drmingdrmer]

Summary

adjust var names; normalize wait_for_xxx utils; add tracing log to key
steps.

Summary about this PR

Changelog

• Build/Testing/CI

Related Issues

#271

[databend-bot]

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[codecov-commenter]

Codecov Report

Merging #651 (a7973f9) into master (aff822b) will decrease coverage by 0%.
The diff coverage is 87%.

@@          Coverage Diff           @@
##           master    #651   +/-   ##
======================================
- Coverage      80%     80%   -1%     
======================================
  Files         289     289           
  Lines       14196   14222   +26     
======================================
+ Hits        11386   11405   +19     
- Misses       2810    2817    +7     

Impacted Files	Coverage Δ
fusestore/store/src/meta_service/raftmeta.rs	65% <55%> (-1%)	⬇️
fusestore/store/src/meta_service/raftmeta_test.rs	94% <100%> (+<1%)	⬆️

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[databend-bot]

CI Passed
Reviewer Approved
Let's Merge