code: function () {
        var innerSelf = this;
  
        return self._readFile()
          .then(function (fileContent) {
            if (fileContent.instances && fileContent.instances[innerSelf._id]) {
              delete fileContent.instances[innerSelf._id];
  
              return self._writeFile(fileContent);
            }
            else {
              debug('delete instance %s not exists for app: %s', innerSelf._id, self._app);
            }
          });
      }
docs: Delete the instance
  
  @returns {Q.promise} promise to finish deleting