CBQE-0: use -Ofair with celery version 3.1.6 on workers

Change-Id: I9214cd1fea7c21bbc3b5196590a301062bbd77f3
Reviewed-on: http://review.couchbase.org/43165
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>