We need to support docker

[timlinux]

Problem

Vagrant is great for local sandbox testing, but we really want to deploy to live servers in docker containers. We should provide an infrastructure for that.

Proposed solution

Implement the following api:

docker(): A convenience function that operates in a similar way to fabtools vagrant.
setup_docker(): Set up docker on the target host.
setup_docker_image(): Set up the default docker image to be used in fabgis deployments.
get_docker_port_mappings(container_id): Given the id of a container, get the ports mapped for that container.
create_docker_container(image='fabgis/sshd'): Create a docker container using the provided base image.

Expected outcome

We should be able to seamlessly deploy fossgis applications into docker containers for a production environment.

CC

@Erve1879