Fix ordering issues using the contain function

Currently, it's possible Puppet will run the `Service['avahi-daemon']` resource before `Package['avahi-daemon']`, which will fail since avahi-daemon won't exist yet. I fixed this by using the contain function introduced in Puppet 3.4: http://docs.puppetlabs.com/puppet/latest/reference/lang_containment.html

Tested with Puppet 3.4.3