Prefer local images for builds, instead of always reaching the hub

While talking with @bparees about adding docker builds to tests we've decided to include this fix to prefer local images instead of always reaching the docker hub. 
The only question we've stumbled upon is how and when to sync those images? So far we've came up with `--sync-images` flag which would also allow to define which images should be synced. What's more important here is also how to sync those while OpenShift is running? Comments welcome...
Use the `env` function.