docs: function loadManifests(dirname, cb) {
      assert.string(dirname, 'dirname');
      assert.func(cb, 'cb');
  
      var self = this;
      var log = self.log;
  
      log.info('loading configuration manifests from %s', dirname);
  
      fs.readdir(dirname, function (err, files) {
          if (err) {
              log.warn(err, 'failed to read directory %s', dirname);
              return (cb(null, []));
          }
  
          vasync.forEachParallel({
              func: function (item, subcb) {
                  loadManifest.call(self,
                      path.join(dirname, item), subcb);
              },
              inputs: files
          }, function (suberr, results) {
              if (suberr)
                  return (cb(suberr));
  
              var result = {};
              results.successes.forEach(function (item) {
                  assert.object(item, 'item');
                  assert.ok(Object.keys(item).length === 1);
  
                  var key = Object.keys(item)[0];
                  result[key] = item[key];
              });
  
              return (cb(suberr, result));
          });
  
          return (null);
      });
  }