Updated templates to use correct format for variables instead of deprecated one

Latest version of Puppet complains about deprecated format for template variables. This commit fixes all warnings.

Here is example of warning message:
```
Warning: Variable access via 'redis_name' is deprecated. Use '@redis_name' instead. template[/vagrant/puppet/modules/redis/templates/etc/init.d/debian_redis-server.erb]:8
   (at /vagrant/puppet/modules/redis/templates/etc/init.d/debian_redis-server.erb:8:in `result')
```