Introduce end-to-end performance tests on medium-sized data

This isn't quite done, but figured it's at a good spot to get feedback.

In particular the cluster security isn't set up correctly yet and thus this hasn't been tested end-to-end.
> I think it might be worth relooking at this at some point (at a minimum the Source(...) part can drop straight into scalaz stream and will tidy up the loop.

Eric had a quick play and it looks like this is broken on our current version of scalaz-stream (runs out of file handles), but in the soon-to-be-released version (on the `append4-final` branch) it's been fixed.