This needs to go away sooner or later, but one complication is the
complex VFIO data structures that are modified in instance_finalize.
Take a shortcut for now.

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>