- image instead of os for models
- Figured out a reasonable way to have a notion of 'latest' image, a
site may have as many image tags as it wants per resource, and those
tags can carry semantics that are enforced by the site. For example a
site could provide 'debian', 'debian-9' and 'debian-8'  image where the
'debian' image simply points to the latest stable release of the distro.

- uuid node search was not recursive, fixed that