Better integration tests

[KristianLyng]

Now that we have influx support, kafka, MQTT, SQL and more, the lack of test-cases that actually use these services is becoming problematic. I never run test cases with SQL, even though they exist.

I/We/Someone needs to look into decent best practices for how to spin up required services to do more extensive tests, to actually ensure our code works. Our test coverage is dropping quickly as more modules are added.

This issue is meant as an interim issue for the over-all problem: Adding integration tests at all. It can be solved when we've got at least one up and running in a way that can be reproduced for other services.