Return set of replica set member addresses.

def _get_replica_set_members(self, selector):
        """Return set of replica set member addresses."""
        # Implemented here in Topology instead of MongoClient, so it can lock.
        with self._lock:
            topology_type = self._description.topology_type
            if topology_type not in (TOPOLOGY_TYPE.ReplicaSetWithPrimary,
                                     TOPOLOGY_TYPE.ReplicaSetNoPrimary):
                return set()

            return set([sd.address for sd in selector(self._new_selection())])