fix #5363: cloudinit: make creation of scsi cloudinit discs possible again

fix #5363: cloudinit: make creation of scsi cloudinit discs possible again

Upon obtaining the device type, a check is performed to determine if it
is a CD drive. It is important to note that Cloudinit drives are always
assigned as CD drives. If the drive has not yet been allocated, the test
will fail due to the unset cd attribute.
To avoid this, an explicit check is now performed to determine if it is
a Cloudinit drive that has not yet been assigned.

Fixes: d1feab4 ("fix #4957: add vendor and product information passthrough for SCSI-Disks")
Signed-off-by: Hannes Duerr <h.duerr@proxmox.com>