update the given dataset client
@param {String} datasetClientId the id of the datasetClient
@param {storage~DatasetClient} fieldsToUpdate the fields to update
@param {Function} callback
function(datasetClientId, fieldsToUpdate, callback) {
      return metrics.timeAsyncFunc(metrics.KEYS.MONGODB_OPERATION_TIME, doUpdateDatasetClient)(datasetClientId, fieldsToUpdate, false, callback);
    }