Description of problem: Some utilities expect a .treeinfo file to be present in the toplevel directory of the iso. Since ovirt-node-ng is derived from boot.iso's, the .treeinfo file is missing.
No need to add this, virt-manager improved its logic for distros without treeinfo in [1] [1] https://github.com/virt-manager/virt-manager/commit/665607fdc203df4f1d6677c702e16f03ca6f0dfa