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/ignore-dependencies.yaml b/tests/fixtures/layouts/ignore-dependencies.yaml
index 9eab9f4..89a82b3 100644
--- a/tests/fixtures/layouts/ignore-dependencies.yaml
+++ b/tests/fixtures/layouts/ignore-dependencies.yaml
@@ -13,6 +13,10 @@
         Verified: -1
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: project1-merge
 
 - job: