Bug 1541821 - Ensure docker images using setup_packages.sh are up-to-date wrt the packages provided there. r=tomprince

When docker images use setup_packages.sh, they add apt sources. While we
currently do run apt-get update to pick those new sources, if a package
provided by them is already installed and not explicitly listed in
subsequent apt-get install, they're not going to be upgraded.

Differential Revision: https://phabricator.services.mozilla.com/D26100

--HG--
extra : moz-landing-system : lando

taskcluster/docker/debian-base/Dockerfile

@@ -31,6 +31,7 @@ CMD ["/bin/bash", "--login"]
 # %ARG DOCKER_IMAGE_PACKAGES
 RUN /usr/local/sbin/setup_packages.sh $TASKCLUSTER_ROOT_URL $DOCKER_IMAGE_PACKAGES && \
     apt-get update && \
+    apt-get dist-upgrade && \
     apt-get install \
       git \
       less \

taskcluster/docker/debian-build/Dockerfile

@@ -27,6 +27,7 @@ RUN dpkg --add-architecture $ARCH
 # use pkg-config, which is multiarch-aware, but we also need dpkg-dev because
 # of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=916772.
 RUN apt-get update && \
+    apt-get dist-upgrade && \
     echo path-exclude=/usr/share/doc/*/changelog.Debian* > /etc/dpkg/dpkg.cfg.d/excludes && \
     if grep -q ^7\\. /etc/debian_version; then \
       BACKPORT=/wheezy-backports; \