feat(py3/py27): integrate pytest-html

In addition to gitlab integration, this one provides quite additional feature:

• display captured stdout/stderr which can been needed for debugging
• is present for everyjob while gitlab integration is only for the MR
• I find the output more useful (because more information) and easier to use that gitlab no so great UI (but less easy to reach)
• it's pretty much free to add

templates/upload-python-package-to-heptapod.yml

+upload-python-package-to-heptapod:
+  stage: publish
+  image: python
+  rules:
+    - if: '$CI_MERGE_REQUEST_ID'
+      when: never
+    - if: '$CI_COMMIT_TAG'
+      when: on_success
+  before_script:
+    - pip install twine
+  script:
+    - python setup.py sdist bdist_wheel
+    - TWINE_PASSWORD=${CI_JOB_TOKEN} TWINE_USERNAME=gitlab-ci-token python -m twine upload --repository-url https://forge.extranet.logilab.fr/api/v4/projects/${CI_PROJECT_ID}/packages/pypi dist/*