Add test for running post playbooks after pre-playbooks fail

Also fix an error this uncovered.

Change-Id: I5bfbe6c64d42bc3e271e3dda2a9c633430238216
diff --git a/tests/fixtures/config/pre-playbook/main.yaml b/tests/fixtures/config/pre-playbook/main.yaml
new file mode 100644
index 0000000..6033879
--- /dev/null
+++ b/tests/fixtures/config/pre-playbook/main.yaml
@@ -0,0 +1,9 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project
+