docker: try to follow the best practices for writing Dockerfiles
Merged multiple RUN instructions and sorted the arguments alphabetically
Reference: https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices/
FROM debian:__CODENAME__
RUN apt-get update && apt-get install -y \
build-essential \
debhelper \
devscripts \
dh-python \
less \
python \
python-all-dev \
python-docutils \
unzip \
zip