VirtualPointerV1Test tests assume server synchonises between send and receive clients

[AlanGriffiths]

Specifically, the incantation:

    send_client.roundtrip();
    receive_client.roundtrip();

Is used with the expectation that when send_client.roundtrip() returns the corresponding events are available to be processed before the receive_client.roundtrip() completes. I don't think there's any reason to expect this.