code: function(callback){
          callback = callback || noop;
  
          if(!this._client){
              return callback();
          }
          this._client.shutdown(function(err){
              if(!this._define_connection){
                  return callback(err);
              }
              this._define_connection.shutdown(function(derr){
                  callback(err || derr);
              });
          }.bind(this));
      }
docs: Chiusura della connessione
  @param  {Function} callback callback