Fix rooms v3 url paths for good - with tests (#1130)

* Fix rooms v3 url paths for good - with tests

- Add a test rig around `federationapi` to test routing.
- Use `JSONVerifier` over `KeyRing` so we can stub things out more easily.
- Add `test.NopJSONVerifier` which verifies nothing.
- Add `base.BaseMux` which is the original `mux.Router` used to spawn public/internal routers.
- Listen on `base.BaseMux` and not the default serve mux as it cleans paths which we don't want.
- Factor out `ListenAndServe` to `test.ListenAndServe` and add flag for listening on TLS.

* Fix comments

* Linting

federationapi/federationapi.go

@@ -35,7 +35,7 @@ func AddPublicRoutes(
 	accountsDB accounts.Database,
 	deviceDB devices.Database,
 	federation *gomatrixserverlib.FederationClient,
-	keyRing *gomatrixserverlib.KeyRing,
+	keyRing gomatrixserverlib.JSONVerifier,
 	rsAPI roomserverAPI.RoomserverInternalAPI,
 	asAPI appserviceAPI.AppServiceQueryAPI,
 	federationSenderAPI federationSenderAPI.FederationSenderInternalAPI,
@@ -44,7 +44,7 @@ func AddPublicRoutes(
 
 	routing.Setup(
 		router, cfg, rsAPI, asAPI,
-		eduAPI, federationSenderAPI, *keyRing,
+		eduAPI, federationSenderAPI, keyRing,
 		federation, accountsDB, deviceDB,
 	)
 }