This creates two modes to run the Docker image:
- either in non-NIGHTLY mode, the latest version will be installed from
pypy.
- or in Nightly mode, it will clone the repository and update it every
time the instance is restarted.
It also updates Python to 3.7, for additional goodness.
- Use exec to run gunicorn and avoid creating a new process.
- Add the possibility to pass any additional parameters to
gunicorn.
- Use only one gunicorn worker by default as the usual way to
scale the app in production would be to use the scale command
of the cluster scheduler. Additional workers could still be
added by passing the "-w" gunicorn parameter to docker run.
