Update patch set 6

Patch Set 6:

So, I made:

1. --push a required argument to push (by default it only builds)
2. parameters (with sensible defaults) for repository name + image prefix. This almost allows us to test this with different images without just pushing to prod and hoping. There is a slight problem however - the Dockerfiles have to mention the name of the image they are inheriting from, and this requires the repo name + prefix be hardcoded! Solution to this probably involves renaming Dockerfiles to Dockerfile.template files, adding those to a .dockerignore file, and generating the Dockerfiles (which should be in .gitignore) from those at runtime and then building. Thoughts on wether that'll be useful? My gut reaction is 'yes' and the added complexity is worth it...

Patch-set: 6