Currently instances with disk_type=scsi are broken, because the SCSI
controller uses a PCI slot not accounted for in the PCI assignment
logic. We reserve a throw-away slot just for that.

This is a temporary workaround and will be reverted during the upcoming
refactoring.

Signed-off-by: Apollon Oikonomopoulos <apoikos@gmail.com>
Signed-off-by: Thomas Thrainer <thomasth@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>