Honor swarm.project.stage as environment variable. Currently swarm.project.stage only is resolved against system property https://github.com/wildfly-swarm/wildfly-swarm/blob/6e257c5f3379f30f4d0a2d9f51ff2c55f05f613e/core/container/src/main/java/org/wildfly/swarm/Swarm.java#L181 but for Docker environments would be awesome to have a resolution against environment variable since this is the way you can pass parameters to docker container.
The property to make it more environment-like name swarm_roject_stage, so code will be something like:
if env swarm_project_stage is present then resolve it
else if sysprop swarm.project.stage is present then resolve it.