Add test for missing CertificateStatus message

If the client sends a status_request extension in the ClientHello
and the server responds with a status_request extension in the
ServerHello then normally the server will also later send a
CertificateStatus message. However this message is *optional* even
if the extensions were sent. This adds a test to ensure that if
the extensions are sent then we can still omit the message.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>