packaging: update Ubuntu docker build dependencies to Python 3 Changeset 7574ccd87200f02e updated the Debian docker builds to Python 3. In doing so, the Ubuntu docker-based builds broke, as the Dockerfile does not include the new dependencies as specified in `contrib/packaging/debian/control`. This commit changes the dependencies in the Ubuntu Dockerfile template to their Python 3 equivalents, fixing `make docker-ubuntu-bionic`. Differential Revision: https://phab.mercurial-scm.org/D7810

FROM ubuntu:%CODENAME%

RUN groupadd -g 1000 build && \
    useradd -u 1000 -g 1000 -s /bin/bash -d /build -m build

RUN apt-get update && apt-get install -y \
  build-essential \
  debhelper \
  devscripts \
  dh-python \
  less \
  python \
  python3-all \
  python3-all-dev \
  python3-docutils \
  unzip \
  zip