Require a base job

This makes base jobs required and allows for a per-tenant default.

Story: 2001110
Task: 4793
Change-Id: I26ffddad8358c156cfac749ce98af70f3447f671
diff --git a/tests/fixtures/layouts/reviews-github.yaml b/tests/fixtures/layouts/reviews-github.yaml
index 1cc887a..f186fbe 100644
--- a/tests/fixtures/layouts/reviews-github.yaml
+++ b/tests/fixtures/layouts/reviews-github.yaml
@@ -12,6 +12,10 @@
           - 'tests passed'
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: project-reviews
 
 - project: