Make the docker export.sh script take an image-name argument

At the moment this script is hardwired to build the base image and the controller. We're now using it elsewhere to build CI containers and we end up having to fork it, it would be great if we could grab a generic script with `curl` and just pass a custom image name and config location to it, rather than having to fork it and edit it in each repo where we want to build a `ce-dev` based container.