Initialise cloud data sync service for specified dataset.
function init(dataset_id, options, cb) {
  debug('[%s] init sync with options %j', dataset_id, options);
  datasets.init(dataset_id, options);
  //make sure we use the exported version here as the start function should be called only ONCE
  module.exports.api.start(function(err) {
    if (err) {
      return cb(err);
    }
    syncStorage.updateManyDatasetClients({datasetId: dataset_id}, {stopped: false}, cb);
  });
}