placement: do not delete orphan peers if some peers selected by RuleFit is down or pending (#4067)

[ti-chi-bot]

This is an automated cherry-pick of #4067

What problem does this PR solve?

fixes #4045

Related changes

• Need to cherry-pick to the release-5.0

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HunDunDM
• nolouch

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[nolouch]

/merge

[ti-chi-bot]

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

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 3e8a5a7

[codecov]

Codecov Report

Merging #4074 (3e8a5a7) into release-5.1 (ca80632) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-5.1    #4074      +/-   ##
===============================================
- Coverage        75.23%   75.15%   -0.08%     
===============================================
  Files              245      245              
  Lines            24594    24600       +6     
===============================================
- Hits             18503    18488      -15     
- Misses            4484     4499      +15     
- Partials          1607     1613       +6     

Flag	Coverage Δ
unittests	75.15% <100.00%> (-0.08%)	⬇️

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

Impacted Files	Coverage Δ
server/schedule/checker/rule_checker.go	82.70% <100.00%> (+1.69%)	⬆️
server/schedulers/shuffle_hot_region.go	55.10% <0.00%> (-10.21%)	⬇️
server/tso/global_allocator.go	70.55% <0.00%> (-5.00%)	⬇️
server/member/member.go	68.81% <0.00%> (-4.31%)	⬇️
server/tso/tso.go	69.66% <0.00%> (-2.81%)	⬇️
server/tso/local_allocator.go	80.55% <0.00%> (-2.78%)	⬇️
client/base_client.go	82.47% <0.00%> (-2.07%)	⬇️
pkg/btree/btree.go	85.30% <0.00%> (-0.97%)	⬇️
server/tso/allocator_manager.go	80.46% <0.00%> (-0.17%)	⬇️
server/grpc_service.go	48.11% <0.00%> (-0.12%)	⬇️
... and 7 more

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