s3: add option to fsync buckets

weed/command/scaffold.go

@@ -76,6 +76,10 @@ const (
 recursive_delete = false
 # directories under this folder will be automatically creating a separate bucket
 buckets_folder = "/buckets"
+buckets_fsync = [          # a list of buckets with all write requests fsync=true
+	"important_bucket",
+	"should_always_fsync",
+]
 # directories under this folder will be store message queue data
 queues_folder = "/queues"