(Optional: for local builds with selenium headless testing) GEB_BUILD_DOCKER_BASE_URL (e.g., "http://docker:9000/redbox", where 'docker' is in /etc/hosts entry created by container to connect to host )
(Optional: if running all containers against a selenium hub and nodes) DOCKER_HUB_URL (e.g., "http://selenium-hub:4444/wd/hub")