server/scheduler: Do not remove the down peer until the normal peers are enough

[AndreMouche]

Signed-off-by: shirly AndreMouche@126.com

What problem does this PR solve?

Issue Number: close #3117

What is changed and how it works?

Do not remove the down peer until the normal peers are enough

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

Release note

Do not remove the down peer until the normal peers are enough

[codecov]

Codecov Report

Merging #3335 (2b573ce) into master (1691df2) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3335      +/-   ##
==========================================
- Coverage   74.81%   74.69%   -0.12%     
==========================================
  Files         243      243              
  Lines       23136    23136              
==========================================
- Hits        17309    17282      -27     
- Misses       4262     4276      +14     
- Partials     1565     1578      +13     

Flag	Coverage Δ
unittests	74.69% <100.00%> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/schedule/checker/replica_checker.go	70.58% <100.00%> (ø)
server/tso/local_allocator.go	74.24% <0.00%> (-7.58%)	⬇️
server/region_syncer/server.go	83.20% <0.00%> (-6.11%)	⬇️
server/id/id.go	76.19% <0.00%> (-4.77%)	⬇️
server/region_syncer/client.go	78.74% <0.00%> (-4.73%)	⬇️
pkg/dashboard/adapter/manager.go	81.52% <0.00%> (-3.27%)	⬇️
server/schedule/operator/step.go	67.44% <0.00%> (-1.67%)	⬇️
server/server.go	71.99% <0.00%> (-0.95%)	⬇️
server/config/persist_options.go	91.33% <0.00%> (-0.79%)	⬇️
server/cluster/coordinator.go	73.57% <0.00%> (-0.72%)	⬇️
... and 9 more

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[Yisaer]

LGTM

[Yisaer]

/merge

[ti-chi-bot]

@Yisaer: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/ti-community-prow repository.

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Details

Commit hash: 12a8d90

[ti-chi-bot]

@AndreMouche: Your PR has out-of-dated, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/ti-community-prow repository.