Allow for Image Id's w/ sha256: Prefix

[johnallen3d]

It would appear that v1.10.0 introduced a change to the image id's. Now when I inspect an image (or container) the id is prefixed with "sha256:".

> docker --version
Docker version 1.9.1, build a34a1d5

> docker inspect alpine:latest
[
    {
        "Id": "3571dd565f47a963b6a35523bd3912aecba747e2a24d1f9be0157c8cf5eb07f2",
        ...
    }
]

> docker --version
Docker version 1.10.0, build 590d5108

> docker inspect alpine:latest
[
    {
        "Id": "sha256:90239124c3524df365bfd1dc0329c383d37f07c22f86e0aaa1f4f00011d56da3",
        ...
    }
]