operator: remove empty JointConsensus steps and fix single voter demote bug (#4534)

[ti-chi-bot]

This is an automated cherry-pick of #4534

Signed-off-by: Hua Lu hua.lu@pingcap.com

What problem does this PR solve?

Closes: #4362
Closes: #4444

What is changed and how it works?

• Modify condition to enable useJointConsensus when there is only single non-demote peer change
• Add logic in execChangePeerV2 to prevent generate empty enter / leave JointConsensus steps
• Remove allowDemote and DemoteFollower step

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

- fix a bug that operate steps may contain unnecessary or empty JointConsensus steps in certain conditions 
- fix a bug when demoting single voter directly

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HunDunDM
• JmPotato

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[codecov]

Codecov Report

Merging #4552 (d2aa67b) into release-5.3 (aec8fd9) will decrease coverage by 0.21%.
The diff coverage is 88.88%.

@@               Coverage Diff               @@
##           release-5.3    #4552      +/-   ##
===============================================
- Coverage        75.04%   74.82%   -0.22%     
===============================================
  Files              264      264              
  Lines            27296    27278      -18     
===============================================
- Hits             20484    20412      -72     
- Misses            5011     5049      +38     
- Partials          1801     1817      +16     

Flag	Coverage Δ
unittests	74.82% <88.88%> (-0.22%)	⬇️

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

Impacted Files	Coverage Δ
server/schedule/operator/step.go	71.87% <ø> (-1.19%)	⬇️
server/schedule/operator/builder.go	86.46% <88.23%> (-2.85%)	⬇️
server/schedule/operator_controller.go	83.84% <100.00%> (-0.89%)	⬇️
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
pkg/tempurl/tempurl.go	45.00% <0.00%> (-15.00%)	⬇️
server/kv/etcd_kv.go	69.56% <0.00%> (-10.15%)	⬇️
server/tso/tso.go	59.09% <0.00%> (-7.96%)	⬇️
server/region_syncer/client.go	79.68% <0.00%> (-3.91%)	⬇️
pkg/etcdutil/etcdutil.go	84.70% <0.00%> (-3.53%)	⬇️
... and 13 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 57c9c2e...d2aa67b. Read the comment docs.

[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

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/tichi repository.

[ti-chi-bot]

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

Commit hash: eb19c1d

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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/tichi repository.