Neutron-lib 1.18.0 is our Rocky RC and is already being used by neutron
. This patch updates the neutron-lib required version to match
neutron  in prep for the Rocky release.
It also adds a lower constraints zuul job to ensure neutron is pulled
into the env; otherwise the errors show in PS1 results will occur.
Configure the layout to execute the scenario004 jobs.
Note that baremetal job will be run on stable/pike and container on
Queens and beyond.
A note has been added in comment explaining more details.