role now fails if specified file not found

fixes https://github.com/ansible/ansible-modules-core/issues/5166

lib/ansible/playbook/role/__init__.py

@@ -207,6 +207,8 @@ class Role(Base, Become, Conditional, Taggable):
             main_file = self._resolve_main(file_path, main)
             if self._loader.path_exists(main_file):
                 return self._loader.load_from_file(main_file)
+            elif main is not None:
+                raise AnsibleParserError("Could not find specified file in role: %s" % main)
         return None
 
     def _resolve_main(self, basepath, main=None):