Add BusType to the libvirt API (DomainGuestInfoFileSystemDisk)

There is an effort in KubeVirt to replace usage of Qemu Agent commands with using libvirt API directly. The project depends on this libvirt-go version, from go.mod:

libvirt.org/go/libvirt v1.10009.1
libvirt.org/go/libvirtxml v1.11000.1

In the response of Domain.GetGuestInfo(libvirt.DOMAIN_GUEST_INFO_FILESYSTEM) it contains FS with Disks and each Disk contains only SerialNumber without BusType that is missing from it.

@pipo.sk opened [PATCH] qemu: Report disk bus as reported by agent in virDomainGetGuestInfo.

Can you please also expose BusType in libvirt-go upon @pipo.sk's patch?