Allow device plugin to list attached and available devices. Enforce
at API level every device being exposed by some domain.
This commit only changes devices API, but not update existing users
(pci) yet.
QubesOS/qubes-issues#2257
This allows the user to start VM based on "old" system (from R3.x) in
R4.0. For example after restoring from backup, or migration. This also
makes upgrade instruction much easier - no need complex recovery
instruction if one upgrade dom0 before upgrading all the templates.
QubesOS/qubes-issues#1812