Start passthrough VM and its dependents by device identity, not address

Adding a PCIe card can renumber the buses behind it, so a hostpci entry
that names a PCI address can pass through the wrong device. These start
the VM only after finding each device by vendor/device/subsystem ID or
by its MAC-pinned interface, repoint its resource mapping if it moved,
and refuse to start on anything ambiguous. Its dependents then wait for
a port on it to answer before starting, so they find their shares up.

systemd-system/passthrough-vm-start.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Start the passthrough VM after checking its PCIe devices
+After=pve-guests.service pve-cluster.service network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=true
+ExecStart=/opt/ergosteur/start-passthrough-vm.sh
+TimeoutStartSec=300
+
+[Install]
+WantedBy=multi-user.target