Set yarn_lock_file_path for zuul-tarball jobs
Set yarn_lock_file_path for zuul-tarball jobs

We need to override the path to our yarn.lock file, as we don't have it
in the top-level directory for zuul.

Change-Id: I356056ef488a77288378e8348468e5ec68ccfe39
Depends-On: https://review.openstack.org/620628
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

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