code: public void addSubsystem(String name, ModelNode settings) throws Exception {
          // /subsystem=<name>:add()
          final ModelNode request = createRequest(ADD, Address.root().add(SUBSYSTEM, name), settings);
          final ModelNode response = execute(request);
          if (!isSuccess(response)) {
              throw new FailureException(response, "Failed to add new subsystem [" + name + "]");
          }
          return;
      }
docs: Adds a new subsystem (along with some optional settings for that subsystem) to the core system
  If settings is null, the subsystem will be created with no additional settings associated with it.
  
  @param name the name of the new subsystem
  @param settings a node with some additional settings used to initialize the subsystem
  @throws Exception any error