service_module: Fixed false positive on initctl as enable_cmd

I have a clean Debian "wheezy" box, added the [dotdeb](http://www.dotdeb.org) repository, and installed `php5-fpm`.

I have the following task:

    - service: "name=php5-fpm enabled=yes state=started"

which fails:

    failed: [debian64.vagrant.malus] => {"failed": true, "item": ""}
    msg: service name not recognized

After some debugging I realized the problem:

The install of `php5-fpm` created the script `/etc/init.d/php5-fpm` (as it should), and `/etc/init/php5-fpm.conf` (not sure why). The latter one causes the `service` module to assume `initctl` is used for enabling the service. But it's not on my box. It should use `update-rc.d`.

This PR fixes that :)

PS: My experience with Debian is very limited.