test: fix incorrect error judging in core_test.go

[jiapengcs]

Ⅰ. Describe what this PR did

correct a mistake in storage/volume/core_test.go, located on line 202, function TestRemoveVolume. After calling core.CreateVolume, we should judge err1, instead of err:

v1, err1 := core.CreateVolume(volid1)
if err != nil {
	t.Fatalf("create volume error: %v", err1)
}

Ⅱ. Does this pull request fix one issue?

fixes #1820

Ⅲ. Describe how you did it

modified the variable from err to err1

Ⅳ. Describe how to verify it

None

Ⅴ. Special notes for reviews

None

[pouchrobot]

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

[pouchrobot]

We found this is your first time to contribute to Pouch, @jiapengcs
👏 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 #1823 into master will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1823      +/-   ##
==========================================
- Coverage    56.3%   56.17%   -0.13%     
==========================================
  Files         200      200              
  Lines       15657    15659       +2     
==========================================
- Hits         8816     8797      -19     
- Misses       5745     5766      +21     
  Partials     1096     1096

Flag	Coverage Δ
#critest	33.52% <ø> (+0.04%)	⬆️
#integrationtest	37.29% <ø> (-0.37%)	⬇️
#unittest	20.32% <ø> (-0.01%)	⬇️

Impacted Files	Coverage Δ
daemon/containerio/hijack_conn.go	77.14% <0%> (-11.43%)	⬇️
daemon/containerio/container_io.go	69.61% <0%> (-4.98%)	⬇️
pkg/meta/store.go	54.76% <0%> (-4.77%)	⬇️
daemon/containerio/options.go	76.19% <0%> (-4.77%)	⬇️
daemon/mgr/container_utils.go	56.27% <0%> (-1.74%)	⬇️
daemon/mgr/system.go	73.27% <0%> (-1.73%)	⬇️
daemon/logger/jsonfile/utils.go	71.54% <0%> (-1.63%)	⬇️
daemon/containerio/cio.go	62.5% <0%> (-1%)	⬇️
daemon/mgr/container.go	53.3% <0%> (+0.15%)	⬆️
cri/v1alpha2/cri.go	66.13% <0%> (+0.17%)	⬆️
... and 2 more

[allencloud]

LGTM