[test-runner] Make transfer/app tests more modular and consistent

[ArjunBhuptani]

App tests should probably be structured very similarly to our app validation libraries:

• At the lowest level we should have some basic app tests that test things like senderDeposit <= freeBalance, which should be done for every app.
• Then we should have a set of tests that is consistent across every transfer app that checks atomicity between hops, consistent params, etc. Should be done for every transfer.
• Lastly we should have specialized tests for each app which check only app-specific failure cases.