This should not be required in version >=4.2.1 as it is already configured into the base install
The ovirt-imageio-proxy allows uploading of image files in the WebGUI. The following step were required for me to get this running.
On oVirt Host
hosted-engine --set-maintenance --mode=global yum install ovirt-imageio-proxy engine-setup
On oVirt Engine
engine-setup engine-config -s ImageProxyAddress=<FQDN of your oVirt Host>:54323 service ovirt-engine restart service ovirt-imageio-proxy restart scp /etc/pki/ovirt-engine/ca.pem root@<ip of your oVirt Host>:/etc/pki/ca-trust/source/anchors/ovirt.ca.pem
On oVirt Host
mkdir /etc/pki/ovirt-engine/ ln -s /etc/pki/ca-trust/source/anchors/ovirt.ca.pem /etc/pki/ovirt-engine/ca.pem hosted-engine --set-maintenance --mode=none
In Browser
http://<FQDN of your oVirt Engine WebGUI>:/ovirt-engine/services/pki-resource?resource=ca-certificate&format=X509-PEM-CA
You should now be able to upload image files in the Storage – Disks area of the oVirt WebGUI.