qemu: Refuse setting <iotune> for 'SD' disks

qemu: Refuse setting <iotune> for 'SD' disks

Historically this didn't work with any supported qemu version as we
don't set the alias of the device, and thus qemu uses a different alias
resulting in a failure to startup the VM:

  internal error: unable to execute QEMU command 'block_set_io_throttle': Device 'drive-sd-disk0' not found

Refuse setting throttling as this is unlikely to be needed and proper
fix requires using -device instead of -drive if=sd.

Note that this was broken when I moved the setup of throttling as a
command at startup for blockdev integration quite a while ago. Until
then throttling was passed as arguments for -drive.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>