Migrate the CI pipeline from Travis to Azure Pipeline (#8098)

Fixes #8071 and fixes https://github.com/certbot/certbot/issues/8110.

This PR migrates every job from Travis in Azure Pipeline.

This PR essentially converts the Travis jobs into Azure Pipeline with a complete iso-fonctionality (or I made a mistake). The jobs are added in the relevant existing pipelines (`main`, `nightly`, `advanced-test`, `release`). A global refactoring thanks to the templating system is done to reduce greatly the verbosity of the pipeline descriptions.

A specific feature (not present in Travis) is added: the stage `On_Failure`. Using directly the Mattermost API, it allows to notify pipeline failure in a Mattermost channel with a link to the failed pipelines without the need to authenticate to Microsoft.

See https://github.com/certbot/certbot/pull/8098#issuecomment-649873641 for the post merge actions to do at the end of this work.

tools/oldest_constraints.txt

@@ -12,7 +12,6 @@ ndg-httpsclient==0.3.2
 ply==3.4
 pyasn1==0.1.9
 pycparser==2.14
-pyOpenSSL==0.13.1
 pyRFC3339==1.0
 python-augeas==0.5.0
 oauth2client==4.0.0
@@ -49,6 +48,7 @@ requests[security]==2.6.0
 
 # Ubuntu Xenial constraints
 ConfigArgParse==0.10.0
+pyOpenSSL==0.15.1
 funcsigs==0.4
 zope.hookable==4.0.4
 

tools/run_oldest_tests.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+set -e
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+
+pushd "${DIR}/../"
+
+function cleanup() {
+  rm -f "${DOCKERFILE}"
+  popd
+}
+
+trap cleanup EXIT
+
+DOCKERFILE=$(mktemp /tmp/Dockerfile.XXXXXX)
+
+cat << "EOF" >> "${DOCKERFILE}"
+FROM ubuntu:16.04
+COPY pipstrap.py /tmp/pipstrap.py
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends \
+        python-dev python-pip python-setuptools \
+        gcc libaugeas0 libssl-dev libffi-dev \
+        git ca-certificates nginx-light openssl curl \
+ && curl -fsSL https://get.docker.com | bash /dev/stdin \
+ && python /tmp/pipstrap.py \
+ && python -m pip install tox \
+ && rm -rf /var/lib/apt/lists/*
+EOF
+
+docker build -f "${DOCKERFILE}" -t oldest-worker ./letsencrypt-auto-source/pieces
+docker run --rm --network=host -w "${PWD}" \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  -v "${PWD}:${PWD}" -v /tmp:/tmp \
+  -e TOXENV -e ACME_SERVER -e PYTEST_ADDOPTS \
+  oldest-worker python -m tox