fix: stop runit services gracefully #44

[q0rban]

Resolves #44

Please read that issue for details of the problem and replication instructions.

Inspired by peterbourgon/runsvinit#3, this aims to solve the issue of stopping services gracefully when the docker container is stopped.

Testing instructions

1. run docker run --rm -it --name tb-test-mariadb-old docker.io/tugboatqa/mariadb
2. Wait for logs to say that mariadb is ready for connections
3. In a separate window, run docker stop tb-test-mariadb-old
4. Note that the logs just end without gracefully shutting down mariadb
5. check out this branch
6. run task -- mariadb
7. run docker run --rm -it --name tb-test-mariadb-new tugboatqa/mariadb
8. wait for logs to say that mariadb is ready for connections
9. in a separate window, run docker stop tb-test-mariadb-new
10. ensure that mariadb shuts down appropriately prior to the container stopping

[q0rban]

@apotek, I would love your thoughts on this! :)

[apotek]

Comments and questions. Nothing blocking.

[rabbitlair]

Tested, it works like a charm!