Create the table underlying the queue.

        Create the 'metadata' and 'tfexample' column families
        and their properties.

def create(self):
        """Create the table underlying the queue.

        Create the 'metadata' and 'tfexample' column families
        and their properties.
        """
        if self.bt_table.exists():
            utils.dbg('Table already exists')
            return

        max_versions_rule = bigtable_column_family.MaxVersionsGCRule(1)
        self.bt_table.create(column_families={
            METADATA: max_versions_rule,
            TFEXAMPLE: max_versions_rule})