workerpool: Fix typo

A call to logging.debug was missing an argument, leading to complaints
on stderr at runtime.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/workerpool.py

@@ -180,7 +180,8 @@ class BaseWorker(threading.Thread, object):
             # Use same priority
             defer.priority = priority
 
-          logging.debug("Deferring task %r, new priority %s", defer.priority)
+          logging.debug("Deferring task %r, new priority %s",
+                        args, defer.priority)
 
           assert self._HasRunningTaskUnlocked()
         except: # pylint: disable-msg=W0702