CASC-232: x-forwarded-host not properly handled when generating service url

Fix for https://issues.jasig.org/browse/CASC-232

Fixes building of service url when X-Forwarded-* headers are present indicating that the request was proxied.  In this case, the service url should be generated for the original request, not the proxied request.
    final URI uri = new URI(serverName);
    String scheme = uri.getScheme();
    String hostname = uri.getHost();
    int port = uri.getPort();