Fixing deprecation notice and updating to instance vars in templates

Simple update to the template to fix this message (run in Puppet 3.3.1).

```
Warning: Variable access via 'locales' is deprecated. Use '@locales' instead. template[/tmp/vagrant-puppet/modules-1/locales/templates/locale.gen.erb]:3
Warning: Variable access via 'default_locale' is deprecated. Use '@default_locale' instead. template[/tmp/vagrant-puppet/modules-1/locales/templates/locale.erb]:2
```