FIX configuration file ownership

[c10l]

Depending on the default ownership and permissions of the Puppet run, the
configuration might be unreadable by the grafana user, causing the service
startup to fail.

One such possible cause is if the file type has default permissions such as:

File {
  owner => 'root',
  group => 'root',
  mode  => '0600',
}

[bastelfreak]

Thanks @cassianoleal!