contrib/docker/debian-jessie

docker: install less as a build-time dependency in deb-based distros

It's needed since 387a76cac28e, otherwise dpkg-checkbuilddeps errors out.

FROM debian:jessie
RUN apt-get update && apt-get install -y \
  build-essential \
  debhelper \
  dh-python \
  devscripts \
  less \
  python \
  python-all-dev \
  python-docutils \
  zip \
  unzip