Collect log output from a tox build

**Role Variables**

.. zuul:rolevar:: zuul_work_dir
   :default: {{ zuul.project.src_dir }}

   Directory tox was run in.

.. zuul:rolevar:: zuul_use_fetch_output
   :default: false

   Whether to synchronize files to the executor work dir, or to copy them
   on the test instance.
   When set to false, the role synchronizes the file to the executor.
   When set to true, the job needs to use the fetch-output role later.


.. zuul:rolevar:: extra_selenium_artifacts_src
   :default: ""

   Optional path on the test node to per-test selenium failure artifacts
   (screenshot.png, page.html, video.mp4). Used by Horizon-based UI plugin
   integration jobs. Leave unset for standard Horizon jobs.

.. zuul:rolevar:: extra_selenium_artifacts_dest
   :default: plugin-selenium

   Subdirectory under logs/tox/ on the Zuul executor for
   extra_selenium_artifacts_src.
