Add php-fpm option

This would configure a vhost to serve php via fpm.

I thought about using the already existing fastcgi solution. But I needed to add an additional location directive to get it all working. So I suppose it might be good to introduce a special php-fpm param that works analogously, but contains this location directive explicitly.

An example would be:

```
nginx::resource::vhost { 'phpmyadmin.mydomain.org':
  ensure => present,
  www_root => '/srv/phpmyadmin',
  ssl => true,
  ssl_key => '/etc/puppet/ssl/private_keys/mymagic.key',
  ssl_cert => '/etc/puppet/ssl/certs/mydomain.org.crt',
  php_fpm => '127.0.0.1:9000',
  rewrite_to_https => true,
  rewrite_www_to_non_www => true,
}
```