tx.go: introduce failpoint before fdatasync

It can be used for power failure cases.

Signed-off-by: Wei Fu <[email protected]>

tx.go

@@ -475,7 +475,7 @@ func (tx *Tx) write() error {
 
 	// Ignore file sync if flag is set on DB.
 	if !tx.db.NoSync || common.IgnoreNoSync {
-		// gofail: var syncWrite struct{}
+		// gofail: var beforeSyncDirtyPages struct{}
 		if err := fdatasync(tx.db); err != nil {
 			return err
 		}
@@ -513,7 +513,7 @@ func (tx *Tx) writeMeta() error {
 		return err
 	}
 	if !tx.db.NoSync || common.IgnoreNoSync {
-		// gofail: var syncMeta struct{}
+		// gofail: var beforeSyncMetaPage struct{}
 		if err := fdatasync(tx.db); err != nil {
 			return err
 		}