fix race in DataReplicatorTest::DataReplicatorResetsOnCompletionCallbackFunctionPointerUponCompletion

If the DataReplicatorTest::DataReplicatorResetsOnCompletionCallbackFunctionPointerUponCompletion test case makes it past the _chooseSyncSource stage and sends a replSetGetRBID request, calling shutdown() without requesting the network interface to deliver the cancellation signal to _rollbackCheckerResetCallback will lead to DataReplicator::join() hanging.