Sort @passenger_cgi_param to make sure generated config file content is stable.

I see a strange issue when I use @passenger_cgi_param in nginx::resource::vhost. The `passenger_set_cgi_param ` part in generated nginx site config is keeping changing. It makes nginx service restarted after every puppet agent run.

It seems `each` on hash map is not stable. My solution is to get hash keys and sort them to make sure it's stable.