fix: correct migrations sorting in getMigrations

[r1tsuu]

What?

We sorted migrations by -name in getMigrations as by assumption from generated file names, however, it may be not true as the improved (+ unflaked, previously it failed sometimes) test for migrate:down can reproduce. As in result, migrateDown / migrateRefresh may execute in order different from migrate.

Unflakes the 'should commit multiple operations async' test.
We shouldn't pass the same req that doesn't contain a transaction to different operations that execute in parallel (via Promise.all) without either creating a transaction before or using isolateObjectProperty(req, 'transactionID'). It leads to a race condition because operation can commit a wrong transaction, different from inited