qemu: Forbid 'cdrom' on 'sd' bus

qemu: Forbid 'cdrom' on 'sd' bus

We can't set the type of the device on the 'sd' bus and realistically a
cdrom doesn't even make sense there. Forbid it.

Note that the output of in disk-cdrom-bus-other.x86_64-latest.args
switched to blockdev as it's no longer locked out due to use of a disk
on 'sd' bus.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>