Fix relationship specification, which fails under Puppet 2.7.11

When using two class names, they get concatenated:

    [ INFO 2014-08-15 09:04:41 verbose] Could not find resource
    'Class[Foreman_proxy::Config]Class[Foreman_proxy::Service]' for relationship
    from 'Class[Puppet::Server::Config]' on node foreman-precise.example.com

Paired with https://github.com/theforeman/puppet-foreman_proxy/pull/115