mm: random test failures in exchange_adaptor_tests.go

[buck54321]

Not always failing, but sometimes.

--- FAIL: TestExchangeAdaptorDeposit (0.20s)
    exchange_adaptor_test.go:1482: not withdrawer, dynamic swapper, token: unexpected pre confirm dex balance. want &{2000000 0 0}, got 2000000

--- FAIL: TestDeposit (0.10s)
    exchange_adaptor_test.go:2386: not withdrawer, dynamic swapper: unexpected post confirm dex balance. want &{1998000 0 0}, got &{1996000 0 0}

[martonp]

These should be fixed now.