Fixes #5845: Add portable init services handling in the Techniques

Ticket: http://www.rudder-project.org/redmine/issues/5845

To be merged in 3.0
It is defined by:
```
    # Autostart ?
      "ovpn_client_autostart" expression => strcmp("&OVPN_CLIENT_AUTOSTART&","true");
```

Actually, I do want to only bootstart ovpn if this class is here :)