Comment 3 for bug 2012979

I think I found where Horizon is pulling the entire image list:

https://github.com/openstack/horizon/blob/76650bbfa7ff3669bde8fdd71f370b66a6be900e/openstack_dashboard/dashboards/project/instances/views.py#L151-L158

To improve performance in an environment with a large number of images, a different approach will be needed.