Add playbook support to simple_layout in tests

All jobs need playbooks, so make sure that we create a stub playbook
for every job which appears in a simple layout.

Move the test_nonvoting_pipeline test to use simple_layout.

Change-Id: Id207fa3c1d01bfaef49f51c86589781b7892585c
diff --git a/tests/unit/test_scheduler.py b/tests/unit/test_scheduler.py
index 366354c..bc84989 100755
--- a/tests/unit/test_scheduler.py
+++ b/tests/unit/test_scheduler.py
@@ -3805,6 +3805,7 @@
         running_items = client.get_running_jobs()
         self.assertEqual(0, len(running_items))
 
+    @simple_layout('layouts/nonvoting-pipeline.yaml')
     def test_nonvoting_pipeline(self):
         "Test that a nonvoting pipeline (experimental) can still report"