Fix path for serial file

It is actually located inside the queue directory.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>

src/Ganeti/Path.hs

@@ -106,7 +106,7 @@ queueDir = dataDirP "queue"
 
 -- | Job queue serial file.
 jobQueueSerialFile :: IO FilePath
-jobQueueSerialFile = dataDirP "serial"
+jobQueueSerialFile = queueDir `pjoin` "serial"
 
 -- | Job queue archive directory.
 jobQueueArchiveSubDir :: FilePath