[TEST] payments mock flow

@geertweening @wltsmrz 

will be cleaning up log output
One thing to test might be payment submission during server state change. If the server is in `disconnected` state, payment submission should fail. If, then, a `serverStatus` event is emitted with `server_state: syncing`, even without ripple-lib's having acquired load/fee information from rippled, a submitted transaction should still serialize with the base fee. I think in this case `LastLedgerSequence` may not be set. Whether this transaction would actually succeed on a live rippled is unclear, but it should serialize and submit anyway.