Add ensure-genmanifest role

Change-Id: Ifebf9da8cd8eeaa9cec621e490064a0f935ddbe0
diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index e4d7397..b1608d1 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -4,3 +4,4 @@
       jobs:
         - test-ensure-web-ext
         - test-install-build-essential
+        - test-ensure-genmanifest