code: function(callback) {
          request.get(
              this.getResourceUrl({ path: '/groups', user: null }),
              function onResourceGroupsResponse(err, res, body) {
                  callback(
                      err,
                      body && body.groups,
                      body && body.search,
                      res
                  );
              }
          );
          return this;
      }
docs: Fetch the resource groups available
  
  @param {Function} callback
  @return {ImboClient}