[web/test] don't delete uicache directory
Other tests use it, so the rmtree was a bit too much. Set CACHEDIR to a
temporary subdirectory, and only delete that.
for table, column in [
('transactions', 'tx_time'),
('tx_entity_actions', 'tx_uuid'),
('tx_relation_actions', 'tx_uuid')]:
repo.system_source.create_index(session, table, column)
commit()