Add job inheritance and start refactoring

This begins a lot of related changes refactoring config loading,
the data model, etc., which will continue in subsequent changes.

Change-Id: I2ca52a079a837555c1f668e29d5a2fe0a80c1af5
diff --git a/tests/fixtures/config/multi-tenant/tenant-two.yaml b/tests/fixtures/config/multi-tenant/tenant-two.yaml
index 57ad64d..6cb2d9a 100644
--- a/tests/fixtures/config/multi-tenant/tenant-two.yaml
+++ b/tests/fixtures/config/multi-tenant/tenant-two.yaml
@@ -1,6 +1,6 @@
 pipelines:
   - name: tenant-two-gate
-    manager: DependentPipelineManager
+    manager: dependent
     success-message: Build succeeded (tenant-two-gate).
     source:
       gerrit
@@ -21,6 +21,10 @@
         verified: 0
     precedence: high
 
+jobs:
+  - name:
+      project2-test1
+
 projects:
   - name: org/project2
     check: