Start uwsgi with `exec` so it receives signals correctly

Ghost User
2019-05-30T12:26:12+02:00

### Short description
[This article](https://hynek.me/articles/docker-signals/) advices to use `exec` when starting docker containers using a shell script.

It makes sure the entrypoint of the docker container receives the signals sent by docker, e.g. when `docker stop` is used.