test: make test more robust

[Letty5411]

Signed-off-by: letty letty.ll@alibaba-inc.com

Ⅰ. Describe what this PR did

This PR mainly fixed some potential failure when tests run in no-travis-CI environment.
For example:

• if the homedir of pouch daemon is not default value, we need to get it dynamically.
• If there is legacy volumes, tests like TestVolumeListOk may fail as it checks there are totally and exactly two volumes.
• If users set test images instead of using default ones, test TestImagesWorks may fail.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #1279 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1279      +/-   ##
==========================================
- Coverage   15.59%   15.57%   -0.02%     
==========================================
  Files         173      178       +5     
  Lines       10819    10454     -365     
==========================================
- Hits         1687     1628      -59     
+ Misses       9013     8706     -307     
- Partials      119      120       +1

Impacted Files	Coverage Δ
daemon/mgr/image_utils.go	0% <0%> (-40%)	⬇️
pkg/reference/def.go	33.33% <0%> (-11.12%)	⬇️
pkg/bytefmt/bytefmt.go	88.88% <0%> (-0.95%)	⬇️
daemon/mgr/cri_utils.go	28.85% <0%> (-0.46%)	⬇️
daemon/mgr/network.go	3.47% <0%> (-0.01%)	⬇️
daemon/mgr/spec.go	0% <0%> (ø)	⬆️
cli/pull.go	0% <0%> (ø)	⬆️
ctrd/container.go	0% <0%> (ø)	⬆️
cli/cli.go	0% <0%> (ø)	⬆️
apis/server/container_bridge.go	0% <0%> (ø)	⬆️
... and 41 more

[fuweid]

LGTM