Add LSB tags and overrides for Debian

Hi,

on a stock Debian Wheezy this module is generating warnings:
 insserv: warning: script 'xvfb' missing LSB tags and overrides
 insserv: warning: script 'x11vnc' missing LSB tags and overrides

The patch corrects this.
Greetz,
Andre
Should we use the variable service name here?  E.g:

```
Provides:      <%= @service %>
```