code: public static ModelNode createRequest(String operation, Address address, ModelNode extra) {
          final ModelNode request = (extra != null) ? extra.clone() : new ModelNode();
          request.get(OPERATION).set(operation);
          request.get(ADDRESS).set(address.getAddressNode());
          return request;
      }
docs: Convienence method that builds a partial operation request node, with additional
  node properties supplied by the given node.
  
  @param operation the operation to be requested
  @param address identifies the target resource
  @param extra provides additional properties to add to the returned request node.
  @return the partial operation request node - caller can fill this in further to complete the node