The dataset client record object
@typedef {Object} storage~DatasetClientRecord
@property {String} uid - the uid of the record
@property {String} hash - the hash value of the data field of the record
@property {Object} data - the actual data of the record
 
List all the dataset clients docs.
@param {Object} filter
@param {Function} cb
function doListDatasetClients(filter, cb) {
  debug('doListDatasetClients');
  var col = mongoClient.collection(DATASETCLIENTS_COLLECTION);
  col.find(filter).toArray(function(err, datasetClients) {
    if (err) {
      debugError('Failed to list datasetClients due to error %s', err);
    }
    return cb(err, datasetClients);
  });
}