Added sync hook (for flash-based roots)

zzz_sync.hook

@@ -0,0 +1,14 @@
+# Force disks to sync to reduce the risk of data corruption
+
+[Trigger]
+Operation = Install
+Operation = Upgrade
+Operation = Remove
+Type = Package
+Target = *
+
+[Action]
+Description = sync all file systems
+Depends = coreutils
+When = PostTransaction
+Exec = /usr/bin/sync