Use Docker in Travis CI to avoid skipping tests

[release-engineering]

Use Docker in Travis CI to avoid skipping tests

[frenzymadness]

I tried to do it and it works!

How I did it:

1. I've created new Docker image called fedora-python-tox designed to run tox tests in Docker container with all available Pythons installed. See github repo and docker hub
2. I've created one more Docker image (designed for Kobo testing) based on Docker image from point one. See Dockerfile in my new docker branch and docker hub
3. Updated .travis.yml file to pull Docker image from point 2 and use it to run test via Tox inside this container. Successful build can be found here
4. As you can see in logs, Python 2.7 and Python 3.6 has no skipped tests.
5. Profit 😄

I can simply reproduce all the steps above or anybody can follow it to create a new Docker hub account, new repository for Kobo, then connecting it with Github and then the last two steps with Dockerfile and Travis configuration (obviously with different names ...).

What do you think about it?

[ktdreyer]

I've filed rpm-py-installer/rpm-py-installer#131 to make it easier to pip install koji on Ubuntu.

[rohanpm]

This was marked closed due to PR #61 which fixes the skipped tests, but note that it didn't do this by using docker. It was sufficient to add some extra steps to the Travis builds to install extra dependencies.