'Create a probe.
:param reactor: Twisted Reactor.
:param control_service: Benchmark control service.
:param UUID dataset_id: UUID for created dataset.
:param int volume_size: Size of created volume, in bytes.
:return: Deferred firing with a new probe.'

@classmethod
def setup(cls, reactor, control_service, dataset_id, volume_size):

    d = control_service.list_nodes().addCallback(select_node)
    def create_probe(node):
        return cls(reactor=reactor, control_service=control_service, primary=node, dataset_id=dataset_id, volume_size=volume_size)
    d.addCallback(create_probe)
    return d
