Scan and assign PCI devices to netvm directly before NetVM start

[joanna]

Currently we scan for NICs and assign them to the default NetVM at install time. This works for most cases, but will not work in the following scenarios:
1) User upgrades their system (not for laptops)
2) User installed Qubes on an external USB driver and now plugged it and booted on a different machine that has different hardware.

[joanna]

But, on the other hand, we should not always assign all devices to each netvm -- some users might wish to use more than one netvm and assign some NICs to netvm #1, and some other to netvm #2, etc.

I think the best way would be to keep in our qubes.xml a property for each netvm whether it should be assigned "all NIC devices" (so is a default and only one netvm), or whether the user decided to assign some select devices to it, in which case we should be updating the .conf files accordingly.

qvm-pref could be used to set which NICs are assigned for each NetVM (by default we would assume a netvm that doesn't have this propery is a default one and get all the NICs on start).

[joanna]

Perhaps we will close this ticker of this as part of getting rid of xend .conf files?

[marmarek]

​http://git.qubes-os.org/gitweb/?p=marmarek/core.git;a=commit;h=7ced90832b83f59d853ced79c8424ce34999109b

PCI devices can by assigned to VMs by qvm-prefs.
Warning: still network devices are assigned to pciback driver at boot time. Only network devices.

(will be changed, when USB controllers will be moved to NetVM/some other VM)