Before installing an OS, nuke everything until it glows.

This also refactors the code handling the OS install boot states
to reduce unneeded noderole transitions.
Merge pull request #253 from VictorLowther/pull-req-master-1861e20532f90489ad0409075a754cdb913aeb53

Have CB2.0 record what disks are where and in use. [2/3]