Collect output from a sphinx build

By default, this copies the output from the sphinx build on the worker
to the log root of the executor.

**Role Variables**

.. zuul:rolevar:: zuul_executor_dest
   :default: {{ zuul.executor.log_root }}

   The destination directory on the executor.  By default, the log
   root.

.. zuul:rolevar:: sphinx_build_dir
   :default: doc/build

   Directory relative to zuul_work_dir where build output will be put.

.. zuul:rolevar:: sphinx_output_suffix
   :default: ''

   Suffix to use for constructing the path. This is normally an
   empty string. If set to '/' then, rsync will remove the last part
   from the original path.

.. zuul:rolevar:: sphinx_output_src
   :default: {{ zuul_work_dir }}/{{ sphinx_build_dir }}/html{{ sphinx_output_suffix }}

   The location on the worker from which to fetch the generated sphinx
   content.  By default, the HTML doc build dir of the current
   project.

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

   The location of the main working directory of the job.

.. 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.