Conditionally notify the nginx service during configuration changes

If you attempt to upgrade nginx/openresty and you have set `node['openresty']['service']['start_on_boot'] = false` you will always receive an error declaring that the `service[nginx]` does not exist in the resource collection. Thus, you must conditionally notify that resource to restart when modifying configuration files.

Additionally, account for a slight difference in `nginx -V` output in Ohai plugin.