Update to Alpine 3.8
Apply best practices eg:
- Don't upgrade
- Add --no-cache-dir to pip install
- Remove removing of any tmp folder as it is deprecated
- Format RUN block nicer
In order to keep the Dockerfile simple, needed opotions have been appended to package provided torrc file and the /etc/init.d/tor script is used to start tor. If further customisation is desired, a wrapper script should be created to have further control on the startup. This would allow things like specifying external (tor) proxies and disable tor startup in those situations.