When executing the tests repo clone in OpenStack-CI,
use zuul-cloner instead of git to enable cross-repo
testing. This ensures that if a dependent patch from
the tests repo is noted using 'Depends-On: <change-id>'
in the commit message, that patch will be included.
Change-Id: If75af45f9ebc17b85bbc8aec019714f4a3625753
Depends-On: Idce7abebf32f24c356a27e099fbca954d917402b