CBQE-1171: fix for ep-engine stat checker

Addresses issues where checking stats from ep-engine postcondition handler always uses default ip:port params.

Change-Id: I60cbf712f9d859ff247bb71827a261bf8c9d72e7
Reviewed-on: http://review.couchbase.org/25349
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>