cluster: fix the merging issue of labels after store reboot

[JmPotato]

What problem does this PR solve?

Issue Number: Close #6467.

What is changed and how does it work?

#5510 introduced a bug that would cause the store labels to be overwritten wrongly after the store reboot.
This PR fixed this issue.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• nolouch
• rleungx

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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: 2bf65db

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #6469.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #6470.

[snowballbear]

I am testing in version v6.5.3.
It turns out that there is only host in the tikv configuration file.
Machine Port Store Status Leaders Regions Capacity Available Labels

---

10.2.8.3
30167 1 Up 21 43 875.8GiB 226.3GiB {host: h2}
30166 4 Up 11 43 875.8GiB 226.3GiB {host: h2}
30168 5 Up 11 43 875.8GiB 226.3GiB {host: h2}

Pd-ctl modified
» config set location-labels zone,host
Success!
» store label 4 zone=us4 host=k4 --rewrite
pd/api/v1/store/4/label?force=true
Success!
» store label 5 zone=us5 host=k5 --rewrite
pd/api/v1/store/5/label?force=true
Success!
» store label 1 zone=us5 host=k1 --rewrite
pd/api/v1/store/1/label?force=true
Success!

tiup cluster display hwtest1 --labels
Machine Port Store Status Leaders Regions Capacity Available Labels

---

10.2.8.3
30167 1 Up 15 43 875.8GiB 226.2GiB {host: k1,zone: us5}
30166 4 Up 9 43 875.8GiB 226.2GiB {host: k4,zone: us4}
30168 5 Up 19 43 875.8GiB 226.2GiB {zone: us5,host: k5}

reload
tiup cluster reload hwtest1
tiup cluster display hwtest1 --labels
Machine Port Store Status Leaders Regions Capacity Available Labels

---

10.2.8.3
30167 1 Up 15 43 875.8GiB 226.3GiB {host: h2,zone: us5}
30166 4 Up 11 43 875.8GiB 226.2GiB {host: h2,zone: us4}
30168 5 Up 17 43 875.8GiB 226.2GiB {zone: us5,host: h2}

After reloading, it was found that the host was restored to its pre-modified state, but the zone was configured. Is this as expected?