In MAKE-SSL-SERVER-STREAM, use the cert file as the key if key isn't specified.
Based on http://tbnl-devel.common-lisp.narkive.com/4DKeC5PZ/hunchentoot-devel-https-server-no-shared-cipher-error via zbeane/zacl#4.
Based on http://tbnl-devel.common-lisp.narkive.com/4DKeC5PZ/hunchentoot-devel-https-server-no-shared-cipher-error via zbeane/zacl#4.