CCBC-234 Add lcb_cntl command to determine source of configuration

Change-Id: I933558ffe4a20eedca6e03ee7bf3d2dfe0e11ab0
Reviewed-on: http://review.couchbase.org/30334
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>