Ensure build script can be used for dev/prod
Ensure build script can be used for dev/prod

There is enough magic going on in the containers without having to keep
track of it in multiple Dockerfiles.

ministryofjustice/mojintranet-theme,ministryofjustice/mojintranet-theme,ministryofjustice/mojintranet-theme,ministryofjustice/mojintranet-theme