bugfix: we should get image ID from containerd

[YaoZengzeng]

Signed-off-by: YaoZengzeng yaozengzeng@zju.edu.cn

Ⅰ. Describe what this PR did

Now we get image ID by calculating ourself, unfortunately it's wrong.

For example busybox:1-uclibc and busybox:1 should have same ID, however:

[root@pouch-test pouch]# pouch images
IMAGE ID       IMAGE NAME                                         SIZE
58af67620523   registry.hub.docker.com/library/busybox:1          710.83 KB
b2e60002262d   registry.hub.docker.com/library/busybox:1-uclibc   709.90 KB

So with this PR we get it directly from containerd then:

[root@pouch-test pouch]# pouch images
IMAGE ID       IMAGE NAME                                         SIZE
8ac48589692a   registry.hub.docker.com/library/busybox:1          710.83 KB
8ac48589692a   registry.hub.docker.com/library/busybox:1-uclibc   709.90 KB

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 #1112 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1112      +/-   ##
==========================================
- Coverage   16.66%   16.66%   -0.01%     
==========================================
  Files         165      165              
  Lines        8911     8918       +7     
==========================================
+ Hits         1485     1486       +1     
- Misses       7321     7326       +5     
- Partials      105      106       +1

Impacted Files	Coverage Δ
daemon/mgr/cri.go	0% <0%> (ø)	⬆️
ctrd/image.go	0% <0%> (ø)	⬆️
client/client.go	25% <0%> (-11.37%)	⬇️
pkg/kernel/kernel.go	72.72% <0%> (-7.28%)	⬇️
cli/command.go	0% <0%> (ø)	⬆️

[YaoZengzeng]

@allencloud PTAL

[allencloud]

I think we need to support tag image, and add an integration test then. @YaoZengzeng

[allencloud]

LGTM