Correct tempest github org.

Should be openstack not openstack-infra.

Change-Id: Ic3bd199373beb082c3ecdeab3b63c0eb1e4154e1
Reviewed-on: https://review.openstack.org/30195
Reviewed-by: Sean Dague <sean@dague.net>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins