Add doc-publisher-site to JJB Tempest project.

JJB broke due to a KeyError on docs-publisher-site when attempting to
build the jobs after we added the tempest docs job. Add a
doc-publisher-site to the tempest project to fix this.

Change-Id: I8f0dcf104ce5f91d0a54848a77e2764cf412d108
Reviewed-on: https://review.openstack.org/30155
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins