Fix Docker installations

`pip` can’t be found, `python-pip` is probably not properly installed

installing `docker-compose` and `docker` from Ubuntu repositories
now available in Ubuntu 16.04 Xenial!

Image deleted as part of GitLab backup shrinking project.
Trying to rebuild the image for jobs which do not define an image to
run with
https://forum.duniter.org/t/migration-de-gitlab-doppler-vega/12459/54