CBQE-1175: use direct mc client for kv latency

replacing previous functionality that relied on underlying sdk,
as latency can be misleading based on implementation.

Change-Id: I62e98c60aab05b3b077a11934e466552b59d4ef5
Reviewed-on: http://review.couchbase.org/25401
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>