Fix conversion of schema 2 manifests to schema 1 manifests

Also adds a number of conversion tests and clarify the interfaces a bit more

image/docker/schema1.py

@@ -267,10 +267,6 @@ class DockerSchema1Manifest(ManifestInterface):
   def image_ids(self):
     return {mdata.v1_metadata.image_id for mdata in self.layers}
 
-  @property
-  def legacy_image_ids(self):
-    return {mdata.v1_metadata.image_id for mdata in self.layers}
-
   @property
   def parent_image_ids(self):
     return {mdata.v1_metadata.parent_image_id for mdata in self.layers
@@ -280,10 +276,6 @@ class DockerSchema1Manifest(ManifestInterface):
   def checksums(self):
     return list({str(mdata.digest) for mdata in self.layers})
 
-  @property
-  def leaf_layer_v1_image_id(self):
-    return self.layers[-1].v1_metadata.image_id
-
   @property
   def leaf_layer(self):
     return self.layers[-1]
@@ -377,7 +369,25 @@ class DockerSchema1Manifest(ManifestInterface):
   def generate_legacy_layers(self, images_map, content_retriever):
     return self.rewrite_invalid_image_ids(images_map)
 
-  def get_v1_compatible_manifest(self, namespace_name, repo_name, tag_name, content_retriever):
+  def get_legacy_image_ids(self, content_retriever):
+    return self.legacy_image_ids
+
+  @property
+  def legacy_image_ids(self):
+    return {mdata.v1_metadata.image_id for mdata in self.layers}
+
+  @property
+  def has_legacy_image(self):
+    return True
+
+  @property
+  def leaf_layer_v1_image_id(self):
+    return self.layers[-1].v1_metadata.image_id
+
+  def get_leaf_layer_v1_image_id(self, content_retriever):
+    return self.layers[-1].v1_metadata.image_id
+
+  def get_schema1_manifest(self, namespace_name, repo_name, tag_name, content_retriever):
     """ Returns the manifest that is compatible with V1, by virtue of being `amd64` and `linux`.
         If none, returns None.
     """