Fix labels warning

[lucklove]

What problem does this PR solve?

Fix #863

What is changed and how it works?

Skip tiflash and tombstone TiKV while fetch labels

Check List

Tests

• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release notes:

NONE

[AstroProfundis]

StoreList() seems redundant for me, the GetStores() is called both in StoreList() and GetStoreLabels(), and it's result is iterated multiple times.

[AstroProfundis]

LGTM

[codecov-io]

Codecov Report

Merging #869 into master will decrease coverage by 0.03%.
The diff coverage is 65.00%.

@@            Coverage Diff             @@
##           master     #869      +/-   ##
==========================================
- Coverage   53.04%   53.00%   -0.04%     
==========================================
  Files         263      263              
  Lines       19038    19030       -8     
==========================================
- Hits        10098    10087      -11     
- Misses       7372     7379       +7     
+ Partials     1568     1564       -4     

Flag	Coverage Δ
#cluster	44.83% <65.00%> (-0.14%)	⬇️
#dm	25.26% <0.00%> (+0.01%)	⬆️
#integrate	47.81% <65.00%> (-0.11%)	⬇️
#playground	22.17% <0.00%> (+<0.01%)	⬆️
#tiup	10.78% <0.00%> (+<0.01%)	⬆️
#unittest	20.95% <50.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
pkg/cluster/manager.go	65.74% <0.00%> (-0.08%)	⬇️
pkg/cluster/spec/spec.go	88.09% <66.66%> (+0.25%)	⬆️
pkg/cluster/api/pdapi.go	53.25% <80.00%> (+1.25%)	⬆️
pkg/cluster/spec/validate.go	93.53% <100.00%> (-1.88%)	⬇️

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