Ubuntu Xenial reached end of standard support almost 6 months ago.
Its default python3 is 3.5, which new versions of many libraries are
dropping support for as that hit EOL earlier this month. We are now
faced with a situation where we cannot test the fetch-sphinx-tarball
role on Xenial because latest SetupTools breaks old funcparserlib
(indirectly needed for our blockdiag and seqdiag elements in
zuul-jobs' docker-image.rst), and the only funcparserlib release
which is installable has dropped Python 3.5 support.
Cease running Ubuntu Xenial platform and Python 3.5 tests for
changes to zuul-jobs now. This is a soft removal, since we're not
actually removing Xenial platform checks from playbooks or roles
yet, nor removing the tox-py35 job definition.
Change-Id: I46b9b887427133147481e92a1e7c523e6592fd2d
9a653e69a6