Error if macaroon key is missing from config

Currently we store all access tokens in the DB, and fall back to that
check if we can't validate the macaroon, so our fallback works here, but
for guests, their macaroons don't get persisted, so we don't get to
find them in the database. Each restart, we generate a new ephemeral
key, so guests lose access after each server restart.

I tried to fix up the config stuff to be less insane, but gave up, so
instead I bolt on yet another piece of custom one-off insanity.

Also, add some basic tests for config generation and loading.

tests/config/test_generate.py

@@ -0,0 +1,50 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# 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.
+import os.path
+import shutil
+import tempfile
+from synapse.config.homeserver import HomeServerConfig
+from tests import unittest
+
+
+class ConfigGenerationTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self.dir = tempfile.mkdtemp()
+        print self.dir
+        self.file = os.path.join(self.dir, "homeserver.yaml")
+
+    def tearDown(self):
+        shutil.rmtree(self.dir)
+
+    def test_generate_config_generates_files(self):
+        HomeServerConfig.load_config("", [
+            "--generate-config",
+            "-c", self.file,
+            "--report-stats=yes",
+            "-H", "lemurs.win"
+        ])
+
+        self.assertSetEqual(
+            set([
+                "homeserver.yaml",
+                "lemurs.win.log.config",
+                "lemurs.win.signing.key",
+                "lemurs.win.tls.crt",
+                "lemurs.win.tls.dh",
+                "lemurs.win.tls.key",
+            ]),
+            set(os.listdir(self.dir))
+        )