registry: add States to retrieve all unit states

@bcwaldon is this in line with what you had in mind? (obviously this doesn't start to split out Jobs() yet, I can do that in this change or a subsequent patch)
I'm not going to know what to do with the `machID` field here when I see this log in the wild. Can you add some context? `...UnitState(%s) from Machine(%s): %v`, perhaps?