Expose image property 'owner' in v2 API

The 'owner' property on an image is exposed in v1 but does not appear in the v2 image response. It would be useful to have this available, e.g., in the case of shared images (the visibility==private, but an image consumer does not actually own the image; if the owner were exposed, you could tell that it was shared (and from whom).

This was discussed at the glance meeting on 16 Jan 2014. The general consensus was that not having the owner exposed was just an oversight in the v2 API.