CCBC-204: Don't use config cache with memcached buckets

Change-Id: Ie355f428f42d09962787da8a8e58ad02509fdab1
Reviewed-on: http://review.couchbase.org/29932
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>