Handle <none>:<none> image about docker-migrate

[jramseye]

Hi! I think I've fixed 1 (just save by IMAGEID:IMAGEID), but I don't really understand 2.
My thoughts:
We only need to save by ID when the image is a : image. Otherwise, we can just save by name:tag. Of the none:none images, each one will have a different image ID. I don't think there is ever a case where two none:none images have the same image ID? If there isn't, then we can just save the none:none images by image ID, and the rest as name:tag, and be fine. (I think?)

[jramseye]

Pushed a fix to 1

[jramseye]

Any thoughts on 2?

[luwensu]

Sorry for the late reply, i thought the scenario too complex(I wanted to cover all supported filesystem ,and after read the docker code, i found it's not related this script......)
I tried it before, lgtm :)

[jramseye]

No worries! Sounds good. Thanks! :)