Run node jobs using version 4 on xenial nodes
Run node jobs using version 4 on xenial nodes

Until such a time as we figure out a strategy off of 4 for these
jobs, we should run them on xenial.

Change-Id: I3c2317cef73f2dda0d047663a0c1c350dd168c72

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