Make selenium v4 syntax optional using the same pattern as
https://review.opendev.org/c/openstack/openstack-helm-infra/+/892708
See:
https: //review.opendev.org/c/openstack/openstack-helm-infra/+/883894/5/grafana/templates/bin/_selenium-tests.py.tpl
Change-Id: I744b721750c474db9fecbd46280d30cfb8347a6f