Create marker table if it doesn't exist.

        Using a separate connection since the transaction might have to be reset.

def create_marker_table(self):
        """
        Create marker table if it doesn't exist.

        Using a separate connection since the transaction might have to be reset.
        """
        if self.marker_table is None:
            self.marker_table = luigi.configuration.get_config().get('sqlalchemy', 'marker-table', 'table_updates')

        engine = self.engine

        with engine.begin() as con:
            metadata = sqlalchemy.MetaData()
            if not con.dialect.has_table(con, self.marker_table):
                self.marker_table_bound = sqlalchemy.Table(
                    self.marker_table, metadata,
                    sqlalchemy.Column("update_id", sqlalchemy.String(128), primary_key=True),
                    sqlalchemy.Column("target_table", sqlalchemy.String(128)),
                    sqlalchemy.Column("inserted", sqlalchemy.DateTime, default=datetime.datetime.now()))
                metadata.create_all(engine)
            else:
                metadata.reflect(only=[self.marker_table], bind=engine)
                self.marker_table_bound = metadata.tables[self.marker_table]