uWGI was generating warnings about being unable to find plugin files we
specify. To fix this, I've added uwsgi-python3 to the list of Alpine
packages we install in the container specified the plugins directory in
the uWSGI config. The updated uWSGI ConfigMap has been applied to the
staging cluster, which eliminated the warning about the logfile plugin.
The remaining warning about the python3 plugin will be eliminated once
the new container built by this branch is deployed.
Dockerfile is now a single multi-stage build that relies on a Python 3.7
base image.
Notes:
- This builds uWSGI with a `pip install` because the Alpine vendored
uWSGI is built against Python 3.6.
- Adds a docker-compose file that can be used for testing that the build
works. It is not usable for development purposes because it creates a
static copy of the application.
