Use official python repository in Dockerfile

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Install test requirements in Dockerfile

Handy for running tests and so on.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Add Makefile for running tests in Docker

It assumes you've got Docker running on /var/run/docker.sock, but
that should be the case on both Linux and in Boot2Docker.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Merge pull request #354 from bfirsh/use-official-repository-for-dockerfile

Add Makefile for running tests in Docker