Update plugin so it can be tested independently

After these small changes, this now works:

    Vagrant::Config.run do |config|
      config.vm.box     = 'precise64'
      ...
      config.vm.provision :puppet do |puppet|
      puppet.manifests_path = "tests"
      puppet.manifest_file  = "plugin.pp"
      puppet.module_path = ["../", "tests/modules/"]
      end
    end