Fix Puppet deprecation warning

Example:

```
Warning: Variable access via 'port' is deprecated. Use '@port' instead. template[/etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb]:6
   (at /etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb:6:in `result')
Warning: Variable access via 'timerpercentile' is deprecated. Use '@timerpercentile' instead. template[/etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb]:21
   (at /etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb:21:in `result')
```