Allow use of Docker for development

Allow use of Docker for development

This makes it possible to use Docker and docker-compose for development
as an alternative to Vagrant.

I quite liked vagrant a couple of years ago, but currently:

 * Trying to install VirtualBox on Ubuntu wants me to disable
   Secure Boot, and I don't want to do that.

 * Trying to use the libvirt plugin for vagrant requires I pick
   from a very small set of possible images, and requires that I
   install the upstream vagrant rather than the vagrant shipped
   with Ubuntu 16.04

 * I find docker containers faster to work with and more transparent.

So I've done the work to make docker work for Patchwork development.
This doesn't break or in any way interfere with using Vagrant, it just
provides an alternative.

It includes support for headless selenium tests using Chromium.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Stephen Finucane <stephenfinucane@hotmail.com>