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.
Depends-On: Idce7abebf32f24c356a27e099fbca954d917402b
Depends-On: I5da7802d61d2ab6b03908138e3a3ed2db22e3d29
Change-Id: Ib9e5f4c93529b6bf74e37ce9f2feb0faa87a3b81