[migration] fix handling of default value for boolean attributes
We can't assert that the old value is 'True' or 'False', because False
used to be stored as an empty string in pre-3.18 versions.
for table, column in [
('transactions', 'tx_time'),
('tx_entity_actions', 'tx_uuid'),
('tx_relation_actions', 'tx_uuid')]:
session.cnxset.source('system').create_index(session, table, column)
commit()