This finalises the ports of the legacy jobs to zuul native jobs.
The dib-setup-gate-mirrors role preconfigures the repo templates,
etc. for the openstack-ci-mirrors element.
The dib-functests role runs the tests as specified by dib_functests,
and can run under python2 or 3.
Change-Id: Ied67a31f0d31503d13eccad8662c29740c93f33e
