puppet-modules-tarball: use zuul-git-prep builder
puppet-modules-tarball: use zuul-git-prep builder

Use zuul-git-prep builder so we clone the repo into WORKSPACE and we can
find the tarball before uploading it.

Co-Authorized-By: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>
Change-Id: Ic38afcb4a3859e1e908946e9f7cce2f7e3535334

openstack-infra/project-config,openstack-infra/project-config