defaults: ide-cd, ide-hd and scsi-cd devices suppress default CD-ROM

ide-hd has to suppress the default CD-ROM, or else you can't put one
on secondary master without -nodefaults.

Unlike legacy scsi-disk, scsi-cd suppresses default CD-ROM.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>