MUPdate support for cosmo

[labbott]

This needs to be validated. At a minimum, wicket needs to know about cosmo.rom

[jgallagher]

This will probably may fall out of adding support to wicket, but just to note it explicitly: Reconfigurator support for host OS updates is in progress now, and it will also need to learn about cosmo.rom. (If this is much larger than whatever we have to do for wicket, we can move this to a separate issue.)

[citrus-it]

It's probably implicit in this but we should begin using "gimlet.rom" for gimlets at the same time.

[labbott]

Fixed by #9038