'Add the storage_policy_index column to the \'container\' table and
set up triggers, creating the policy_stat table if needed.
:param conn: DB connection object'

def _migrate_add_storage_policy_index(self, conn):

    try:
        self.create_policy_stat_table(conn)
    except sqlite3.OperationalError as err:
        if ('table    policy_stat    already    exists' not in str(err)):
            raise
    conn.executescript(('\n                                                ALTER    TABLE    container\n                                                ADD    COLUMN    storage_policy_index    INTEGER    DEFAULT    0;\n                                ' + POLICY_STAT_TRIGGER_SCRIPT))
