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/repo-checkout-four-project.yaml b/tests/fixtures/layouts/repo-checkout-four-project.yaml
index 36937e9..17303f5 100644
--- a/tests/fixtures/layouts/repo-checkout-four-project.yaml
+++ b/tests/fixtures/layouts/repo-checkout-four-project.yaml
@@ -33,6 +33,10 @@
     precedence: high
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: integration
     required-projects:
       - org/project1