MB-100: introduced menelaus_util:reply_404/1

Change-Id: I57d8d1ab2829a70dcd85a64b94c8656393880f1e
Reviewed-on: http://review.couchbase.org/27942
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>