Run CI on more distributions

Background

This has been an ongoing bit of work for a while now. Time to create an issue!

We currently support tests for:

• (Debian 8 (to be deprecated))
• Debian 9
• Fedora 27

These simply happen to be the distributions most used among core developers, which isn't a great way to determine what to test on.

Task description

We should add additional images for a few more distributions. The following spring to mind (feel free to suggest more):

• Ubuntu 18.04 (current LTS)
• Fedora 28 (current)
• Arch

Acceptance Criteria

We would like to both have identified important targets and implemented the CI for them.

---