This gets rid of the warning message saying that nothing is actually
linking to the document.
To get rid of the chicken-egg problem:
The -infra templated job for docs requires that a venv be created using
tox. It will actually run this command to build the documentation:
tox -evenv -- python setup.py build_sphinx
Change-Id: I0f03ad6efe2a997c9cecac6240e1e8be8e85ccf6