Don't override flush state on exit

pvcd.py

@@ -46,6 +46,7 @@ def cleanup():
     t_node[myhostname].stop()
     time.sleep(0.2)
     try:
+        if t_node[myhostname].getstate() != 'flush':
             zk.set('/nodes/' + myhostname + '/state', 'stop'.encode('ascii'))
         zk.stop()
         zk.close()