HttpsConnectorFactory fails to compile with Java 8

Hi,

`HttpsConnectorFactory` fails to compile with Java 8 because it uses the `sun.security.x509.CertAndKeyGen` class which was moved to the `sun.security.tools.keytool` package.

`CertAndKeyGen` is used to generate a self signed certificate dynamically when no certificate was specified. This could be fixed by using reflection, but I think it's better to drop this functionality since it is fundamentally insecure. If the certificate changes every time the server is started it's impossible to add an exception and trust the certificate. Users will be presented with a new certificate and won't be able to tell if it's normal or if someone intercepted the connection.