Add a test for a broken config on startup

We currently log an exception and then exit, requiring operator
intervention.

Change-Id: I39f7a0fea7c59776d929718fb4116e62d23d25cc
diff --git a/tests/fixtures/config/broken/main.yaml b/tests/fixtures/config/broken/main.yaml
new file mode 100644
index 0000000..a22ed5c
--- /dev/null
+++ b/tests/fixtures/config/broken/main.yaml
@@ -0,0 +1,6 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-repos:
+          - common-config