feat(instances): PCI devices of the host given to a shut-off VM

- The Host devices tab gives a shut-off VM a PCI device of its host and
  takes it back; libvirt binds the device to vfio-pci when the VM starts
  and gives it back when it stops (managed). The VM's PCI devices are
  listed with whether the running VM and its next start have them.
- A device is offered, and accepted on the server under the compute's
  claim, only when it is no bridge of any kind (bridge header, PCIe port,
  or of the bridge class: host bridge, LPC), the host has none of its own
  network interfaces, disks or graphics card on it (else: bind it to
  vfio-pci on the host first), no other VM names it, and every other
  endpoint of its IOMMU group is the VM's too or has no driver or
  vfio-pci and no other VM; bridges in the group stay with pcieport, and
  a member that cannot be read keeps the group. Nothing in the group is
  taken implicitly.
- A snapshot revert checks the PCI devices of the snapshot with the same
  rules; migration and clones already leave host devices out.
- The add forms of the tab load together, when the tab opens.

instances/tests/test_console_settings_access.py

@@ -61,7 +61,7 @@ class ConsoleSettingsAccessTestCase(TestCase):
             proxy.get_max_memory.return_value = 4096
             proxy.get_networks.return_value = []
             proxy.get_ifaces.return_value = []
-            proxy.get_hostdevs.return_value = ([], [])
+            proxy.get_hostdevs.return_value = ([], [], [])
             proxy.get_storages.return_value = []
             proxy.get_console_passwd.return_value = VNC_PASSWORD
             proxy.get_console_type.return_value = "vnc"