Use alpine python and gunicorn

Adding docker_settings.py which reads environment variables
to allows for environment variable to be passed to the
container

Dockerfile

@@ -1,3 +1,12 @@
-FROM grahamdumpleton/mod-wsgi-docker:python-2.7-onbuild
-CMD [ "wsgi.py" ]
+FROM python:2.7-alpine
 
+ENV PUPPETBOARD_PORT 80
+ENV PUPPETBOARD_SETTINGS docker_settings.py
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+
+COPY requirements-docker.txt /usr/src/app/
+RUN pip install --no-cache-dir -r requirements-docker.txt
+COPY . /usr/src/app
+
+CMD gunicorn -b 0.0.0.0:${PUPPETBOARD_PORT} --access-logfile=/dev/stdout puppetboard.app:app