bugfix: do not append latest to image name having a tag already

[yyb196]

Ⅰ. Describe what this PR did

when using swarm to pull an image, it post a request with a param named fromImage, which already include a tag, then we shouldn't append a 'latest' to it.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

fixes #1109

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[allencloud]

Could we add a test case to cover to avoid future change still make the error happen again?

[yyb196]

@allencloud yes, I will setup some test case to protect it.

[codecov-io]

Codecov Report

Merging #1110 into master will decrease coverage by 1.23%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1110      +/-   ##
==========================================
- Coverage   16.67%   15.43%   -1.24%     
==========================================
  Files         165      171       +6     
  Lines        8912     9569     +657     
==========================================
- Hits         1486     1477       -9     
- Misses       7320     7984     +664     
- Partials      106      108       +2

Impacted Files	Coverage Δ
apis/server/image_bridge.go	21.53% <100%> (ø)
pkg/kernel/kernel.go	50% <0%> (-22.73%)	⬇️
daemon/mgr/container_utils.go	56.19% <0%> (-1.85%)	⬇️
daemon/mgr/container.go	5% <0%> (-0.01%)	⬇️
client/container.go	0% <0%> (ø)	⬆️
daemon/mgr/spec.go	0% <0%> (ø)	⬆️
daemon/mgr/spec_linux.go	0% <0%> (ø)	⬆️
client/container_create.go
apis/server/server.go	0% <0%> (ø)
apis/server/volume_bridge.go	0% <0%> (ø)
... and 7 more

[yyb196]

@allencloud I have added an unit test case to protect this modification, PTAL again.

[allencloud]

Actually I could not follow the unit test you add. Maybe I need your guidance offline. @yyb196

[allencloud]

LGTM, this is for swarm part legacy API calling.