test: add unit-test for toCriSandbox

[MarkLux]

Ⅰ. Describe what this PR did

add unit-test for toCriSandbox

Ⅱ. Does this pull request fix one issue?

fixes #1915

Ⅲ. Describe how you did it

add testcases with normal and error

Ⅳ. Describe how to verify it

run go test -v -run toCriSandbox

Ⅴ. Special notes for reviews

[pouchrobot]

@MarkLux Thanks for your contribution. 🍻
Please sign off in each of your commits.

[pouchrobot]

We found this is your first time to contribute to Pouch, @MarkLux
👏 We really appreciate it.
Just remind that you have read the contribution guide: https://github.com/alibaba/pouch/blob/master/CONTRIBUTING.md
If you didn't, you should do that first. If done, welcome again and please enjoy hacking! 🍻

[pouchrobot]

ping @MarkLux
We found that this PR is 22 commits, which is more than 10 commits, behind master.
Please rebase the branch against master and push it back again. Thanks a lot.

[codecov-io]

Codecov Report

Merging #2002 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2002      +/-   ##
==========================================
+ Coverage   63.31%   63.41%   +0.09%     
==========================================
  Files         200      200              
  Lines       15522    15552      +30     
==========================================
+ Hits         9828     9862      +34     
+ Misses       4455     4453       -2     
+ Partials     1239     1237       -2

Flag	Coverage Δ
#criv1alpha1test	33.86% <ø> (+0.01%)	⬆️
#criv1alpha2test	34.4% <ø> (+0.12%)	⬆️
#integrationtest	38.54% <ø> (+0.1%)	⬆️
#unittest	21.18% <ø> (+0.32%)	⬆️

Impacted Files	Coverage Δ
cri/v1alpha1/cri.go	65.4% <0%> (-0.19%)	⬇️
cri/v1alpha1/cri_utils.go	76.07% <0%> (+1.78%)	⬆️
ctrd/watch.go	78.12% <0%> (+2.36%)	⬆️