Description of problem:
Create a VM from registry and edit its disk, the prefix "docker://docker://" was added to its value.
If not edit the disk, no this problem.

Version-Release number of selected component (if applicable):
v4.12.0

How reproducible:
100%

Steps to Reproduce:
1. create vm from catalog
2. move to customize mode
3. select registry as the disk source and fill the value like "registry.redhat.io/rhel8/rhel-guest-image"
4. move to review page and click disks tab
5. edit the rootdisk, the container image value becomes "docker://registry.redhat.io/rhel8/rhel-guest-image", which is not correct, it should stay with "registry.redhat.io/rhel8/rhel-guest-image"
6. save and create the vm
7. review the VM yaml, the registry value is 'docker://docker://registry.redhat.io/rhel8/rhel-guest-image'

Actual results:
The status of the VM is DataVolumeError, because it cannot import the container image "docker://docker://registry.redhat.io/rhel8/rhel-guest-image"

Expected results:
VM is started

Additional info: