BUG: Docker download for Ubuntu fails non-deterministically

[flongford]

The current method of downloading and installing docker on Ubuntu is done via gpg / keyservers (https://github.com/simphony/simphony-remote/blob/master/Makefile#L18)

Every so often the installation will fail (see an example log), with the error message gpg: keyserver receive failed: No data

This looks to be a known IPv4 vs. IPv6 issue, and so we should implement some best practices (see below) to avoid failures as much as possible since it has resulted in many wasted Travis builds

nodejs/docker-node#380

docker-library/official-images#4252