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/common.yaml b/tests/fixtures/config/multi-tenant/common.yaml
index d36448e..8fc3bba 100644
--- a/tests/fixtures/config/multi-tenant/common.yaml
+++ b/tests/fixtures/config/multi-tenant/common.yaml
@@ -1,6 +1,6 @@
 pipelines:
   - name: check
-    manager: IndependentPipelineManager
+    manager: independent
     source:
       gerrit
     trigger: