Cockpit Machines can now share a host directory with a guest virtual machine

Cockpit Machines can provide this sharing feature, providing the semantics and performance of the local file system.

- Virtiofs is available in Linux 5.4, QEMU 5.0 and libvirt 6.2. Host file sharing is only available when these versions are available.

- The virtual machine details page now shows the list of USB, PCI and SCSI host devices that are transmitted to the guest VM.

- Enabling "network export" allows a Redis data source with the pmproxy service