parameter not set in ds-identify causes failure in nocloud or uvt-kvm with iso on non-cdrom as seed

[Scott Moser]

The fix for bug 1731868 left a interim change in ds-identify referencing an undeclared variable.

That code path would be hit if you attached an ISO filesystem to a device other than a cdrom.
For example:

qemu-system-x86_64 -enable-kvm \
  -device virtio-net-pci,netdev=net00 \
  -netdev type=user,id=net00 \
  -drive file=disk.img,id=disk00,if=none,format=qcow2,index=0 \
  -device virtio-blk,drive=disk00,serial=disk.img \
  -drive file=my-seed.img,id=disk01,if=none,format=raw,index=1 \
  -device virtio-blk,drive=disk01,serial=my-seed.img \
  -m 768 -nographic

It would work fine if you attached the iso filesystem as a cdrom.
(-cdrom my-seed.img)