[bug] Pouch can't find correct image to create container while using repoDigest

[faycheng]

Ⅰ. Issue Description

Pouch can't find correct image to create container while using repoDigest.

In Scenario 1，pouch created container with unexpected image

➜  ~ pouch images
IMAGE ID       IMAGE NAME                                     SIZE
4493f9e1fd39   registry.hub.docker.com/library/nginx:latest   42.46 MB
➜  ~ pouch run -d registry.hub.docker.com/library/fake_image@sha256:c4ee0ecb376636258447e1d8effb56c09c75fe7acf756bf7c13efadf38aa0aca
f6befab19d384e54202cd0b637f343cc7b3ec309245ecab379b57446195d3a9d
➜  ~ pouch inspect -f '{{.Image}}' f6befab19d384e54202cd0b637f343cc7b3ec309245ecab379b57446195d3a9d
registry.hub.docker.com/library/nginx:latest

In Scenaria 2, failed to create container caused by too many images

➜  ~ pouch images
IMAGE ID       IMAGE NAME                                      SIZE
786f81bbee21   registry.hub.docker.com/library/alpine:latest   1.97 MB
4493f9e1fd39   registry.hub.docker.com/library/nginx:latest    42.46 MB
➜  ~ pouch run -d registry.hub.docker.com/library/fake_image@sha256:c4ee0ecb376636258447e1d8effb56c09c75fe7acf756bf7c13efadf38aa0aca
Error: failed to run container: {"message":"image: : too many"}

Ⅱ. Describe what happened

Ⅲ. Describe what you expected to happen

Ⅳ. How to reproduce it (as minimally and precisely as possible)

Ⅴ. Anything else we need to know?

Ⅵ. Environment:

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[pouchrobot]

Thanks for your contribution. 🍻 @faycheng
While we thought ISSUE TITLE could be more specific, longer than 20 chars.
Please edit issue title instead of opening a new one.
More details, please refer to https://github.com/alibaba/pouch/blob/master/CONTRIBUTING.md

[YaoZengzeng]

@faycheng Thanks for your issue.

Actually the code of pouch's image is complicated and confusing and it will be hard to maintain in the future.

So I refactor the related code and make the rule more simple #973 , also fix the bug in this issue.

Thanks again for your issue and would you like to convert it into a test case in test/cli_images_test.go ? :)

[faycheng]

@YaoZengzeng Thanks for your reply.
And i will create a pr to convert this issue into a test case.