job to build sphinx documentation (python job)

'{name}-sphinx-doc' will simply run:

 python setup.py build_sphinx

The resulting documentation is not published anywhere though :(

Generate jobs:

mw-tools-codeutils-sphinx-doc
mw-tools-fluoride-sphinx-doc
mw-tools-release-sphinx-doc
mwext-BlameMaps-sphinx-doc
mwext-ConfirmEdit-sphinx-doc
mwext-DumpHTML-sphinx-doc
mwext-EventLogging-sphinx-doc
mwext-Offline-sphinx-doc
mwext-OpenStackManager-sphinx-doc
mwext-SemanticBundle-sphinx-doc
mwext-SemanticResultFormats-sphinx-doc
mwext-WikimediaMaintenance-sphinx-doc
operations-debs-adminbot-sphinx-doc
operations-debs-ircecho-sphinx-doc
operations-dumps-sphinx-doc
operations-software-redactatron-sphinx-doc
operations-software-sphinx-doc
pywikibot-compat-sphinx-doc
pywikibot-core-sphinx-doc
pywikibot-i18n-sphinx-doc
sartoris-sphinx-doc
wikimedia-fundraising-tools-sphinx-doc

Although most of them will NOT be triggered.

Change-Id: I5ba1a17662905d8ab30dcabe18b5b6374f9aea05