Use fqdn for ssl listen address instead of clientcert

Chris Barker reported that the default value of `$::clientcert`
was not the best choice for some things we were using it for
in the module; specifically, for the default value of
the jetty ssl listen address.  He suggested using `$::fqdn` instead.

This commit makes that change; rspec-system tests pass, but I'm
not 100% sure that there aren't edge cases that would be
affected by this.