Description of problem:
When trying to use a DV as a lun with
disks:

• lun:
  bus: virtio
  name: rootdisk

where rootdisk is a DVT in a VM, then I get:

Error "spec.template.spec.domain.devices.disks[0].lun can only be mapped to a PersistentVolumeClaim volume." for field "spec.template.spec.domain.devices.disks[0].lun".

Version-Release number of selected component (if applicable):
4.12

How reproducible:
Always

Steps to Reproduce:
1. Create a VM
2. Adjust one disk backed by a DV to use a lun instead of disk
3. Save

Actual results:
Error "spec.template.spec.domain.devices.disks[0].lun can only be mapped to a PersistentVolumeClaim volume." for field "spec.template.spec.domain.devices.disks[0].lun".

Expected results:
Works

Additional info: