### 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
e176b8b764