qemuBuildDeviceAddresDriveProps: Prepare for 'drive' address for usb-bot disks

qemuBuildDeviceAddresDriveProps: Prepare for 'drive' address for usb-bot disks

While the 'usb-storage' based disks use the USB address directly, with
'usb-bot' the USB address is on the "controller" part of the device and
the 'scsi-hd/cd' device will use a 'drive' address from qemu's PoV.

Since we do not want to expose the 'usb-bot' as explicit controller
to preserve compatibility with existing configs we plan to upgrade
implement the formatter for 'drive' address when the "diskbus" property
is VIR_DOMAIN_DISK_BUS_USB.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>