need to fix a bug in TestBPOfferService#waitForBlockReceived that fails the trunk, e.g. in Build #1781.
Details: in this test, the utility function waitForBlockReceived() has a bug:
parameter mockNN is never used but hard-coded mockNN1 is used.
This bug introduces undeterministic test failure when testBasicFunctionality() calls
ret = waitForBlockReceived(FAKE_BLOCK, mockNN2);
and the call finishes before the actual interaction with mockNN2 happens.