Fix for age calculation on unused nodes

Setting the node state automatically changes the state_time
attribute for us, so our age calculation is always at 0 when
we go to log how old the node is at delete time. Fix it so
that we set state *after* logging the age.

Change-Id: I6e0510405f43842529c733110378b96decb88a07

nodepool/zk.py

@@ -1691,10 +1691,10 @@ class ZooKeeper(object):
                 self.unlockNode(node)
                 continue
 
-            node.state = DELETING
             try:
                 self.log.debug("Deleting unused node %s (age: %s)",
                                node.id, age(node.state_time))
+                node.state = DELETING
                 self.storeNode(node)
             except Exception:
                 self.log.exception(