*: refine error log in cluster pkg (#2868)

[ti-srebot]

cherry-pick #2868 to release-4.0

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Signed-off-by: Howard Lau howardlau1999@hotmail.com

What problem does this PR solve?

To solve #2704

Check List

Tests

• Unit test

Release note

• No release note

[lhy1024]

/run-all-tests

[rleungx]

/cc @howardlau1999

[ti-srebot]

@howardlau1999,Thanks for your review. The bot only counts LGTMs from Reviewers and higher roles, but you're still welcome to leave your comments.See the corresponding SIG page for more information. Related SIG: scheduling(slack).

[rleungx]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[rleungx]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[howardlau1999]

/merge

[ti-srebot]

/run-all-tests

[codecov]

Codecov Report

Merging #2906 into release-4.0 will increase coverage by 0.46%.
The diff coverage is 13.63%.

@@               Coverage Diff               @@
##           release-4.0    #2906      +/-   ##
===============================================
+ Coverage        77.37%   77.84%   +0.46%     
===============================================
  Files              210      210              
  Lines            22793    22803      +10     
===============================================
+ Hits             17637    17750     +113     
+ Misses            3825     3721     -104     
- Partials          1331     1332       +1     

Impacted Files	Coverage Δ
server/api/middleware.go	75.00% <0.00%> (ø)
server/handler.go	51.19% <0.00%> (+0.43%)	⬆️
server/kv/etcd_kv.go	82.27% <0.00%> (+8.86%)	⬆️
server/schedule/plugin_interface.go	20.00% <0.00%> (+0.95%)	⬆️
server/server.go	76.82% <0.00%> (-0.75%)	⬇️
server/cluster/coordinator.go	70.33% <8.00%> (+0.31%)	⬆️
server/cluster/cluster.go	83.75% <12.50%> (+2.84%)	⬆️
server/core/storage.go	72.86% <20.00%> (-0.57%)	⬇️
pkg/etcdutil/etcdutil.go	86.30% <33.33%> (-5.25%)	⬇️
server/schedule/scheduler.go	65.30% <44.44%> (-4.47%)	⬇️
... and 18 more

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