loader: don't hard-code mainRouter in loadApps

This was causing a new test to fail, as it could not properly load APIs
on a custom muxer. This was simply never spotted as loadApps is always
passed mainRouter in the production code.

api_definition_test.go

@@ -106,7 +106,6 @@ func createDefinitionFromString(defStr string) *APISpec {
 	loader := APIDefinitionLoader{}
 	def := loader.ParseDefinition(strings.NewReader(defStr))
 	spec := loader.MakeSpec(def)
-	spec.APIDefinition = def
 	return spec
 }
 

api_loader.go

@@ -552,7 +552,7 @@ func loadApps(specs []*APISpec, muxer *mux.Router) {
 					"api_name": spec.Name,
 					"domain":   spec.Domain,
 				}).Info("Custom Domain set.")
-				subrouter = mainRouter.Host(spec.Domain).Subrouter()
+				subrouter = subrouter.Host(spec.Domain).Subrouter()
 			}
 			chainObj := processSpec(spec, apisByListen, redisStore, redisOrgStore, healthStore, rpcAuthStore, rpcOrgStore, subrouter)
 			chainObj.Index = i