After c07d1c1c got merged it uncovered couple of broken domain
XMLs for bhyvexml2argv test. Some disk drives had incompatible
type of address configured.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

Automatically allocate PCI addresses for devices instead
of hardcoding them in the driver code. The current
allocation schema is to dedicate an entire slot for each devices.

Also, allow having arbitrary number of devices.

At this point unittest covers 4 basic cases:

 - minimal working XML for bhyve
 - same as above, but with virtio disk
 - ACPI and APIC args test
 - MAC address test