CBD-1410: track max. memcached RSS in revAB test

Change-Id: Idfdd805b30d45289a78fbde824f2eae9622fc5aa
Reviewed-on: http://review.couchbase.org/40123
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>