test(integration): Correctly cleanup logs

[provokateurin]

Summary

While running the integration tests locally I found a few problems that are fixed by this:

• The tail is never killed, so when you run the command again you get 2x, 3x, ... the same logs
• The previous logs are not removed, so you see the logs from previous runs as well which can be confusing
• If the script is killed while still running (e.g. Ctrl+C) the background processes aren't killed

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)