The FSYNC_WAL flag does not work on branch-2.x

You can check the reference to SyncFuture.isForceSync, no one calls it. And in FSHLog, we always use the field useHsync instead of getting one from the SyncFuture. I think the problem here is that we have done some optimization for batching the sync futures on branch-2.x so it is not easy to get the forceSync flag from a single SyncFuture when doing sync.

But anyway, we need to fix this.