Cleanup method doesn't run on docker container shutdown

Not 100% sure what's going on here, but I think it's either that the SIGINT doesn't get sent at all when docker shuts the container down, or that the process isn't allowed enough time to clean up.

This leads to lost time for users.

https://stackoverflow.com/questions/41451159/how-to-execute-a-script-when-i-terminate-a-docker-container