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

internal/test/keyring.go

@@ -0,0 +1,31 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package test
+
+import (
+	"context"
+
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// NopJSONVerifier is a JSONVerifier that verifies nothing and returns no errors.
+type NopJSONVerifier struct {
+	// this verifier verifies nothing
+}
+
+func (t *NopJSONVerifier) VerifyJSONs(ctx context.Context, requests []gomatrixserverlib.VerifyJSONRequest) ([]gomatrixserverlib.VerifyJSONResult, error) {
+	result := make([]gomatrixserverlib.VerifyJSONResult, len(requests))
+	return result, nil
+}