machines: libvirt D-Bus provider: Add EventListener for close signal on libvirt-dbus service

[KKoukiou]

@Antique pointed out that it's good idea to have an EventListener on close signal for libvirt-dbus. The service might crash or for some reason stop. libvirt-dbus will get restarted but we need to handle the change in the client and restart event monitoring on the new client.

This issue asumes cockpit-project/cockpit#9240 is merged.

[marusak]

@KKoukiou this has not been yet implemented, right?

[KKoukiou]

No it's not implemented - It should not be hard though. We already have the same logic for libvirtd

[KKoukiou]

This is edge case scenario and will not be implemented unless requested.