qemu: Refuse blockjobs on disk bus='sd' with -blockdev

qemu: Refuse blockjobs on disk bus='sd' with -blockdev

We still have to use -drive to instantiate sd disks. Combining that with
the new logic for blockjobs would be very complicated and not worth it
given that 'sd' cards work only on few rarely used machine types of
non-common architectures and libvirt didn't implement support for 'sd'
bus controllers. This will allow us to use -blockdev for other kinds on
such machines while sacrificing block jobs.

Note: this is currently no-op as we mask-out the QEMU_CAPS_BLOCKDEV
capability if any of the disks has bus='sd'.

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