CBQE-0: AttributeError: Queue instance has no attribute 'pop'

Queue.empty() not reliable

Change-Id: I84e6b99aca228b7d52dba8fbccf2c6f788fbcfe5
Reviewed-on: http://review.couchbase.org/35645
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>