Make sure to decode manifests into utf-8 when necessary

This fixes a decoding error

image/docker/schemas.py

@@ -10,6 +10,13 @@ def parse_manifest_from_bytes(manifest_bytes, media_type, validate=True):
   """ Parses and returns a manifest from the given bytes, for the given media type.
       Raises a ManifestException if the parse fails for some reason.
   """
+  # NOTE: Docker sometimes pushed manifests encoded as utf-8, so decode them
+  # if we can. Otherwise, treat the string as already unicode encoded.
+  try:
+    manifest_bytes = manifest_bytes.decode('utf-8')
+  except:
+    pass
+
   if media_type == DOCKER_SCHEMA2_MANIFEST_CONTENT_TYPE:
     return DockerSchema2Manifest(manifest_bytes)