Add unit-tests for dm-master/worker failover/scaler/upgrader and some other components

[lichunzhu]

What problem does this PR solve?

#2868
Add UT part 2.
supplement for #3310

What is changed and how does it work?

1. add unit tests for dm-master/worker failover/scaler/upgrader
2. add unit tests for dmcluster used components, including orphanPodsCleaner, pvcResizer, reclaimPolicyManage

Check List

Tests

• Unit test
• E2E test

Code changes

• Has Go code change

Does this PR introduce a user-facing change?:

NONE

[lichunzhu]

Will be able to be reviewed after #3310 is merged.

[codecov-commenter]

Codecov Report

Merging #3326 into master will increase coverage by 8.31%.
The diff coverage is 67.25%.

@@            Coverage Diff             @@
##           master    #3326      +/-   ##
==========================================
+ Coverage   42.15%   50.46%   +8.31%     
==========================================
  Files         159      159              
  Lines       16436    16511      +75     
==========================================
+ Hits         6928     8333    +1405     
+ Misses       8867     7400    -1467     
- Partials      641      778     +137     

Flag	Coverage Δ
#unittest	50.46% <67.25%> (?)

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[DanielZhangQD]

LGTM