Use import from six.moves to import the queue module

The name of the synchronized queue class is queue instead of
Queue in Python3.

Change-Id: I508268561f95c9fed2d39fb45731aab5d9d74111

nodepool/task_manager.py

@@ -18,7 +18,7 @@
 
 import sys
 import threading
-import Queue
+from six.moves import queue as Queue
 import logging
 import time