test: add unit test for func storage/volume/ListVolumeName

[btlcmr0702]

Ⅰ. Describe what this PR did

add unit test for func storage/volume/ListVolumeName at core_test.go

Ⅱ. Does this pull request fix one issue?

YES, for #1763

Ⅲ. Describe how you did it

Get all the name of volume by the func ListVolumeName and then try to find whether they are the same with name of volume.

Ⅳ. Describe how to verify it

Run go test at dir storage/volume

Ⅴ. Special notes for reviews

TEAM 10
baiji developers

[CLAassistant]

All committers have signed the CLA.

[pouchrobot]

We found this is your first time to contribute to Pouch, @btlcmr0702
👏 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! 🍻

[codecov-io]

Codecov Report

Merging #1810 into master will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1810      +/-   ##
==========================================
+ Coverage    56.3%   56.42%   +0.12%     
==========================================
  Files         200      200              
  Lines       15657    15657              
==========================================
+ Hits         8816     8835      +19     
+ Misses       5745     5730      -15     
+ Partials     1096     1092       -4

Flag	Coverage Δ
#critest	33.5% <ø> (+0.02%)	⬆️
#integrationtest	37.67% <ø> (+0.01%)	⬆️
#unittest	20.37% <ø> (+0.04%)	⬆️

Impacted Files	Coverage Δ
apis/server/utils.go	61.9% <0%> (-4.77%)	⬇️
cri/v1alpha2/cri.go	66.13% <0%> (+0.17%)	⬆️
daemon/mgr/container.go	53.46% <0%> (+0.31%)	⬆️
ctrd/container.go	50.17% <0%> (+1.37%)	⬆️
daemon/mgr/system.go	76.72% <0%> (+1.72%)	⬆️
ctrd/image.go	78.71% <0%> (+1.98%)	⬆️
storage/volume/core.go	62.43% <0%> (+2.92%)	⬆️