Code review comment for lp:~mvo/launchpad-buildd/mvo

I think it would be odd to move buildlivefs outside of launchpad-buildd and not the corresponding helpers for other build types, and buildlivefs's interface is quite closely tied to launchpad-buildd so it would be nice not to end up overcomplicating our deployments, especially as buildds have historically been stuck on old Ubuntu releases (maybe this will change with scalingstack, but let's see). I don't mind making buildlivefs friendlier for occasional non-launchpad-buildd use; I'd just prefer this not to involve things that might be less resilient to bugs elsewhere in production.