Core should automaticaly unbind all pci devs that are assigned to a VM that is being started

[marmarek]

Besides, we should, I think, implement some better pci dev management
support in qubes.py. E.g. the QubesVM class should offer methods such as
add_pci_dev(), get_pci_devs(), revoke_pci_dev().

Then it would be trival to write a useful supporting tools, such as:
qvm-lspci, qvm-add-pci-to-vm, qvm-revoke-pci-from-vm.

The current scheme (treating all the pcidevs as a argument string) is
not very fortunate -- qvm-pref is not able to detect simple errors (such
as missing quotation mark, and it also makes it harder to automatically
unbind all the pci devs assigned to VMs.

[marmarek]

1. PCI devices assigned to VM are bound to pciback at VM start
2. new tool qvm-pci

​http://git.qubes-os.org/gitweb/?p=marmarek/core.git;a=commit;h=5f10e408e0ba6145b94f9eb187456efa4cd54dc9