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

Change-Id: Ib11a79e73c28b0387dde2f94092c3bc1c23269b4
Reviewed-on: http://review.couchbase.org/36330
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>