CBQE-0: fix task manager and vbucket None issue

Change-Id: I78b82511ff861249ea6f137923b6d174602560e7
Reviewed-on: http://review.couchbase.org/35673
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>