Fix dm-master restarted failed; add scale E2E cases

[csuzhangxc]

What problem does this PR solve?

• fix dm-master pods may not be restarted #3971
• add scale out/in E2E tests cases, part of Support DM 2.0 in TiDB Operator #2868

What is changed and how does it work?

fix --join arg for DM-master

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

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

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

Fix the issue that DM-master may restart failed

[codecov-commenter]

Codecov Report

Merging #3972 (4b4c1f8) into master (37e0a14) will increase coverage by 4.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3972      +/-   ##
==========================================
+ Coverage   61.99%   66.09%   +4.09%     
==========================================
  Files         173      177       +4     
  Lines       18342    18844     +502     
==========================================
+ Hits        11371    12454    +1083     
+ Misses       5859     5201     -658     
- Partials     1112     1189      +77     

Flag	Coverage Δ
e2e	31.13% <ø> (?)
unittest	61.98% <ø> (-0.02%)	⬇️

[csuzhangxc]

https://ci.pingcap.net/job/tidb-operator-pull-e2e-kind/41/display/redirect failed may be caused by pingcap/dm#1671

[DanielZhangQD]

LGTM

[handlerww]

/run-all-tests

[handlerww]

LGTM

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• DanielZhangQD
• handlerww

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[csuzhangxc]

/merge

[ti-chi-bot]

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

Commit hash: 4b4c1f8