[libvirt] Qemu: create empty cdrom

[Gromak Yuriy]

Hello.
Qemu is latest from master branch.
Tryingto start a domain, which is connected toa blankcdrom:

         <disk type='file' device='cdrom'>
           <driver name='qemu' type='raw'/>
           <target dev='sdb' bus='scsi'/>
           <readonly/>
           <address type='drive' controller='0' target='1' bus='0' 
unit='0'/>
         </disk>

But I get an error:

qemu-system-x86_64: -drive 
if=none,id=drive-scsi0-0-1-0,readonly=on,format=raw: Can't use 'raw' as 
a block driver for the protocol level.