[feature request] create container using image ID with digest algorithm prefix

[YaoZengzeng]

Ⅰ. Issue Description

Docker is able to run a container using image ID with digest algorithm prefix as follows:

[root@VM_68_206_centos pouch]# docker inspect busybox
[
    {
        "Id": "sha256:8ac48589692a53a9b8c2d1ceaa6b402665aa7fe667ba51ccc03002300856d8c7",
        "RepoTags": [
            "docker.io/busybox:latest"
        ],
       .....
}
[root@VM_68_206_centos pouch]# docker run -it sha256:8ac48589692a53a9b8c2d1ceaa6b402665aa7fe667ba51ccc03002300856d8c7
/ # 

But pouch can't:

[root@VM_68_206_centos ~]# pouch image inspect busybox
[
    {
        "Architecture": "amd64",
        "Config": {
            "Cmd": [
                "sh"
            ],
        .....
        "Id": "sha256:8ac48589692a53a9b8c2d1ceaa6b402665aa7fe667ba51ccc03002300856d8c7",
        .....
}
]
[root@VM_68_206_centos ~]# pouch run sha256:8ac48589692a53a9b8c2d1ceaa6b402665aa7fe667ba51ccc03002300856d8c7
Error: failed to run container: {"message":"image: registry.hub.docker.com/library/sha256:8ac48589692a53a9b8c2d1ceaa6b402665aa7fe667ba51ccc03002300856d8c7: not found"}

We need this feature as k8s 1.10+ will use image inspect to get the image ID, and then use it to create container. However the image ID get from image inspect has digest algorithm prefix like sha:

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: