CCBC-395: Provide lcb_cntl() API for configuration cache

Change-Id: I8c45f2a62887945e6bb6925702bfbd05deb964db
Reviewed-on: http://review.couchbase.org/36419
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>