test: add test cases for mountpoint_test.go and portbindngs_test.go

[sanmaopep]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

Merging #2583 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2583      +/-   ##
==========================================
- Coverage   69.18%   69.17%   -0.02%     
==========================================
  Files         278      278              
  Lines       18689    18689              
==========================================
- Hits        12930    12928       -2     
- Misses       4285     4288       +3     
+ Partials     1474     1473       -1

Flag	Coverage Δ
#criv1alpha1test	31.38% <ø> (+0.15%)	⬆️
#criv1alpha2test	35.69% <ø> (-0.1%)	⬇️
#integrationtest	40.71% <ø> (-0.05%)	⬇️
#nodee2etest	32.77% <ø> (+0.02%)	⬆️
#unittest	26.74% <ø> (+0.07%)	⬆️

Impacted Files	Coverage Δ
pkg/streams/utils.go	82.14% <0%> (-9.53%)	⬇️
cri/v1alpha2/cri_wrapper.go	64.4% <0%> (-1.2%)	⬇️
cri/v1alpha2/cri.go	69.48% <0%> (-0.13%)	⬇️
cri/v1alpha1/cri.go	60.59% <0%> (+0.33%)	⬆️
ctrd/container.go	59.28% <0%> (+0.39%)	⬆️
apis/server/utils.go	75% <0%> (+3.84%)	⬆️
apis/opts/portbindings.go	100% <0%> (+19.04%)	⬆️

[sanmaopep]

@ZYecho Thanks for your suggestions, I will modify them 😄

[ZYecho]

LGTM
wait for CI pass

[allencloud]

Thanks for your great work.
@sanmaopep
Wish you have a great journey to participant in community.
In addition, we have a dingtalk group which contains almost all the develops and contributors of PouchContainer. Would you like to join us?