Switch to yaml.safe_load

We only deal with simple types.

Change-Id: Ic902b19dc8db9d0e1e3dab0909dfd2400a169c49
diff --git a/tests/unit/test_layoutvalidator.py b/tests/unit/test_layoutvalidator.py
index 38c8e29..319bfaa 100644
--- a/tests/unit/test_layoutvalidator.py
+++ b/tests/unit/test_layoutvalidator.py
@@ -56,7 +56,7 @@
             connections = zuul.lib.connections.configure_connections(config)
 
             layout = os.path.join(FIXTURE_DIR, 'layouts', fn)
-            data = yaml.load(open(layout))
+            data = yaml.safe_load(open(layout))
             validator = zuul.layoutvalidator.LayoutValidator()
             if m.group(1) == 'good':
                 try: