Correctly register publisher artefacts with router

Publisher will set the owning_app to "publisher", and the rendering_app
to "frontend". This means that the router will route requests to
frontend.*.alphagov.co.uk rather than publisher.*.alphagov.co.uk

app/models/enhancements/artefact.rb

@@ -3,5 +3,5 @@
 class Artefact
   # Add a non-field attribute so we can pass indexable content over to Rummager
   # without persisting it
-  attr_accessor :indexable_content, :paths, :prefixes
+  attr_accessor :indexable_content, :paths, :prefixes, :rendering_app
 end

app/models/routable_artefact.rb

@@ -15,8 +15,8 @@ def router
   end
 
   def ensure_application_exists
-    backend_url = Plek.current.find(@artefact.owning_app)
-    router.update_application(@artefact.owning_app, backend_url)
+    backend_url = Plek.current.find(rendering_app)
+    router.update_application(rendering_app, backend_url)
   end
 
   def submit
@@ -27,10 +27,15 @@ def submit
       paths << @artefact.slug
     end
     paths.uniq.each do |path|
-      @router.create_route(path, "full", @artefact.owning_app)
+      @router.create_route(path, "full", rendering_app)
     end
     prefixes.each do |prefix|
-      @router.create_route(prefix, "prefix", @artefact.owning_app)
+      @router.create_route(prefix, "prefix", rendering_app)
     end
   end
+
+  private
+    def rendering_app
+      @artefact.rendering_app || @artefact.owning_app
+    end
 end