code: static void parseSubsystems(ModelNode node, List<Subsystem> subsystems) {
          List<Property> properties = node.get("subsystem").asPropertyList();
          for (Property property : properties) {
              Subsystem subsystem = new Subsystem(property.getName(), property.getValue());
              subsystems.add(subsystem);
          }
      }
docs: Expects a "subsystem" child resource. Modeled as a static helper method to make it usable from both
  deployments and subdeployments.