CBQE-2233: add expire pager run before waiting stats

Change-Id: I93658475aa70796c9360cd85960fed4829ebe8c1
Reviewed-on: http://review.couchbase.org/37172
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>