Allow to auto-generate self-signed SSL certificates

The setup is rather simple. Instead of a full-blown CA, a CSR is used to create the self-signed certificate.

PKI certificates are only generated on non-SUSE platforms, (open)SUSE provides PKI certs via it's packages. Since by default the SSL certs will be identical to PKI certs, we can only check for their existance if they have been generated. 

Only allow to generate SSL certs if all paths to SSL keyfile / certfile (and ca_certs) are different from the PKI cert paths. If they're the same, there's no need to auto-generate further self-signed certificates.