Fix schema1 manifest etag and docker content digest header

When schema2 manifests are rewritten as schema1 currently the etag and docker content digest header keep the value for the schema2 manifest.

Fixes #1444

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

docs/handlers/images.go

@@ -196,6 +196,7 @@ func (imh *imageManifestHandler) convertSchema2Manifest(schema2Manifest *schema2
 		imh.Errors = append(imh.Errors, v2.ErrorCodeManifestInvalid.WithDetail(err))
 		return nil, err
 	}
+	imh.Digest = digest.FromBytes(manifest.(*schema1.SignedManifest).Canonical)
 
 	return manifest, nil
 }