Hello,
I'll do my best to help you with that but first let's look closely into your situation. Specifically I have two questions:
1) What exactly was the issue when you tried to upload the ISO to data domain? I've just tried that on oVirt 4.3.7 and has no problem with it.
2) Can you double check that you've got the right cloud image? As far as I know cloud images are usually provided in QCOW2 format, like here:
https://cloud.centos.org/centos/7/images/ Do you
need to use ISO files at all?
Best regards
Jan