code: function() {
  
      debug('shutting down...');
  
      var app = this;
      var server = this.server;
  
      if (!server) return Promise.resolve();
  
      return co.wrap(function* () {
        yield this.hookFor('shutdown');
      }).call(this).then(function() {
        server.close(function() { debug('goodbye!'); });
      });
  
    }
docs: gracefully stop the http(s) server and close after requests are complete.
  @return {void}