No support for image with namespace and tag

I encountered an issue where if I was attempting run a container from an image that was in a private repository, and the image was prefixed with a namespace and a tag is provided, then it would fail.

I have added a test for this and updated the image name parser to accept an arbitrary number of "sub-directories" as namespaces.  This doesn't appear to be true to the spec but perhaps some larger organizations may divide their images by organization/project, 

e.g.
    example.registry.com:5000/org/team/image:1.0