Currently, bhyvexml2xmltest does only one test. We can do better.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

In the next patch we will need a stable mac address for
<interface/>.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

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>

Don't use duplicating target dev names.

Rather than just picking the first CD (or failing that, HDD) we come
across, if the user has picked a boot device ordering with <boot
order=''>, respect that (and just try to boot the lowest-index device).

Adds two sets of tests to bhyve2xmlargv; 'grub-bootorder' shows that we
pick a user-specified device over the first device in the domain;
'grub-bootorder2' shows that we pick the first (lowest index) device.

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