Add a Status field on ImageRepository

When clients want to use internal ImageRepositories (an ImageRepository that is backed by an OpenShift registry that can be automatically created on demand when a user pushes or pulls to it) a client needs to be able to know what registry URL that is in order to push images.

This pull adds a Status struct to an ImageRepository (as defined upstream, a set of attributes that represent the current condition of a resource) that conveys the *real* DockerImageRepository name (vs the value set on creation or update by a consumer).  It is populated when Get/List is called and defaults to a value set by an ENV attribute (although discussion in https://github.com/GoogleCloudPlatform/kubernetes/issues/1319 is leaning towards a service with a known name and namespace).

When a client requests an ImageRepository, the "status.dockerImageRepository" will be set to "dockerImageRepository" or to the value of `<defaultRegistry>/<namespace>/<name>`.  A properly configured default registry would know how to lookup `<namespace>/<name>` when pulling the image.

@ncdc review
Copied verbatim from upstream - didn't want to change it


> On Dec 1, 2014, at 9:25 AM, Andy Goldstein <notifications@github.com> wrote:
> 
> In pkg/image/api/helper.go:
> 
> > +	if len(parts) == 2 {
> > +		repo = parts[0]
> > +		image = parts[1]
> > +	}
> > +	parts = strings.SplitN(image, ":", 2)
> > +	if len(parts) == 2 {
> > +		image = parts[0]
> > +		tag = parts[1]
> > +	}
> > +	if repo != "" {
> > +		image = fmt.Sprintf("%s/%s", repo, image)
> > +	}
> > +	return image, tag
> > +}
> > +
> > +// parseRepositoryTag gets a repos name and returns the right reposName + tag
> I'd either do repo or repository, but not repos
> 
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