CBQE-0 add exception catcher in warmup test.

Change-Id: Id75c3278bb9f4d140293d913239e33a99f82d51e
Reviewed-on: http://review.couchbase.org/39965
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>