CBQE-0: optimizations in verify_xdcr_stats & _expiry_pager

for xdcr part unjustified timeouts we have here

Change-Id: I4115c49fe72e23317720cee3806b59327dd78151
Reviewed-on: http://review.couchbase.org/32848
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>