Improve api functional tests performance

[ygrishajev]

Currently we have to run tests sequentially utilising jest's --runInBand option. This is to avoid DB data checks and master wallet sequence mismatch. It would be great to address these issues and run tests in parallel. This way we'd save our own time running tests locally, consume less of CI resources and reduce PR checks time.

DB acceptance criteria:

• create new dbs for every test run
• override relevant env vars
• drop dbs after finish

Master wallet acceptance criteria:

• generate a new wallet for a test run
• send tokens to the every wallet created
• override relevant env vars

[ygrishajev]

As DB part is pretty trivial, wallet part might need some thinking. Some points I'm concluding so far:

• It might be a good idea to store wallets into some json file checked into git, to avoid wallet creation on every run
• The above also would reduce frequency of funding if implemented properly
• Every run should lock the cached wallet