function schemas(connection) {
    return getDatastoreClient(connection).schemas(connection).catch(logError);
}
schemas retrieves a list of table names, column names and column data types
@param {object} connection Connection object
@returns {Promise.<object>} that resolves to the results as:
  {
      columnnames: [...],
      rows: [[table_name, column_name, data_type], ...]
  }