cluster: enable service after scale out

[9547]

What problem does this PR solve?

fix #875

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[codecov-io]

Codecov Report

Merging #905 (651de0c) into master (92d6fab) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #905      +/-   ##
==========================================
- Coverage   53.50%   53.45%   -0.05%     
==========================================
  Files         263      263              
  Lines       19072    19063       -9     
==========================================
- Hits        10205    10191      -14     
- Misses       7294     7299       +5     
  Partials     1573     1573              

Flag	Coverage Δ
cluster	45.46% <100.00%> (-0.04%)	⬇️
dm	25.23% <ø> (-0.09%)	⬇️
integrate	48.29% <100.00%> (-0.06%)	⬇️
playground	22.26% <ø> (ø)
tiup	10.84% <ø> (ø)
unittest	21.12% <0.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
components/cluster/command/scale_out.go	89.47% <100.00%> (+19.26%)	⬆️
pkg/utils/retry.go	42.10% <0.00%> (-15.79%)	⬇️
components/dm/command/scale_out.go	85.18% <0.00%> (-7.41%)	⬇️
pkg/cliutil/ssh.go	16.21% <0.00%> (-2.71%)	⬇️
pkg/cluster/api/dmapi.go	58.26% <0.00%> (-1.74%)	⬇️
pkg/cluster/spec/tikv.go	55.61% <0.00%> (-1.54%)	⬇️
pkg/cluster/api/pdapi.go	60.99% <0.00%> (-0.31%)	⬇️

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