Explicitly use Chef::Provider::Service::Debian on Ubuntu/Debian

The next version of Chef will use Chef::Provider::Service::Upstart by
default in Ubuntu 13.10+ [Changelog], [CHEF-5276]), because Ubuntu
stopped shipping compatibility links in /etc/init.d/ [bug], [wiki].

[Changelog] https://github.com/opscode/chef/blob/master/CHANGELOG.md
[CHEF-5276] https://tickets.opscode.com/browse/CHEF-5276
[bug] https://bugs.launchpad.net/ubuntu/+source/rsyslog/+bug/1311810/comments/4
[wiki] https://wiki.ubuntu.com/UpstartCompatibleInitScripts