The Docker image now defaults to the tutor production settings, which allows us
to remove the environment variable from the docker-compose and k8s
configuration files.
Since we introduced `tutor dev quickstart`, we must be able to initialize the
discovery container in dev mode. The problem is that the "openedx" partner is
unavailable in dev mode. Thus, we need to default to the "dev" partner in dev
mode.
Close#33.
