vm-configurator: Introduce hack to fix regression in audio
Libvirt 7.2.0 (2021-04-01) added support for audio backend specific settings. See https://libvirt.org/news.html
Boxes uses libvirt-glib to manipulate libvirt domain configurations, and libvirt-glib doesn't have yet a GVirConfig.DomainAudio device.
This is a temporary fix/hack that edits the VM configuration XML directly to replace the audio.type and audio.serverName properties of the xml node. This DOES NOT test for the existence or support of the audio backend.
See #738 (closed)