Cannot override base image selection when creating agent ISO

It's not currently possible to override the base image selected by the command:

$ openshift-install agent create image

Also defining the OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE variable does not have any effect 

4.14

By defining the OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE when creating the image

1. $ OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE=<valid url to rhcos image> 
2. $ openshift-install agent create image
3.
 

The agent ISO is built by using the embedded rhcos.json metadata, instead of the rhcos image specified in the OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE

Defining OPENSHIFT_INSTALL_OS_IMAGE_OVERRIDE should allow overriding the base image selected for creating the agent ISO