Travis continuous integration using Docker

[AndreMiras]

It would be great if Travis testing was running in a Docker container.
That would make it easier to reproduce broken builds locally. Hence speed up debugging, increase overall stability and encourage external contributions.
We could reuse most of the work of the existing Dockerfile.

I've already done something similar, see my Dockerfile. That would also simplify the Travis config, see my Travis config on green build. The config is basically just a docker build and docker run (with a make test). All the logic being in the Docker image.

I would suggest to use Ubuntu LTS as a base:

FROM ubuntu:16.04

What do you guys think? If you are interested, let me know and I can come up with a pull request.