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/basic-github.yaml b/tests/fixtures/layouts/basic-github.yaml
index 709fd02..d7b323a 100644
--- a/tests/fixtures/layouts/basic-github.yaml
+++ b/tests/fixtures/layouts/basic-github.yaml
@@ -18,7 +18,12 @@
       github: {}
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: project-test1
+
 - job:
     name: project-test2