Method waitAndSync

fdbserver/DiskQueue.actor.cpp:126–131

	Reference<IAsyncFile> file;

	ACTOR static Future<Void> waitAndSync(SyncQueue* self) {
		wait(self->outstanding.front());
		self->outstanding.pop_front();
		wait(self->file->sync());
		return Void();
	}
};

// We use a Tracked instead of a Reference when the shutdown/destructor code would need to wait() on pending file