[WIP] Testing with multiple versions of Conda

[colin-nolan]

This PR improves the testing such that the module is tested against multiple version of Conda. This should help us keep this module working with future versions of Conda, at the same time of maintaining compatibility with previous versions.

The change moves from running the Ansible based tests on one Docker instance against itself to using Docker compose to setup a test runner and multiple target machines, each of which has different versions of Conda/Python installed.

[colin-nolan]

Seems to be a problem with running this in Travis CI...