This patch does a few things to fix the documentation builds for
this project
- Move requirements to doc/requirements.txt for building docs to
avoid installing extra dependencies.
- Bump sphinx version to a newer release which is compatible with
sphinxcontrib-programoutput
- Remove default theme option to use the latest Sphinx theme that
is shipped directly from upstream.
- Bumped basepython for documentation jobs to Python 3.
These are all squashed because the job is currently broken.
Change-Id: Ib998923a5daaa5e9d3ddc748b76b6304e5c39b22
a4449758bf