Adjustments based on code review feedback

image/docker/schema2/manifest.py

@@ -140,6 +140,10 @@ class DockerSchema2Manifest(ManifestInterface):
       if layer.is_remote and not layer.urls:
         raise MalformedSchema2Manifest('missing `urls` for remote layer')
 
+  @property
+  def is_manifest_list(self):
+    return False
+
   @property
   def schema_version(self):
     return 2