Make sure to decode manifests into utf-8 when necessary

This fixes a decoding error

test/registry/protocols.py

@@ -81,6 +81,7 @@ class ProtocolOptions(object):
     self.push_by_manifest_digest = False
     self.request_addr = None
     self.skip_blob_push_checks = False
+    self.ensure_ascii = True
 
 
 @add_metaclass(ABCMeta)
@@ -120,7 +121,7 @@ class RegistryProtocol(object):
   def conduct(self, session, method, url, expected_status=200, params=None, data=None,
               json_data=None, headers=None, auth=None, options=None):
     if json_data is not None:
-      data = json.dumps(json_data)
+      data = json.dumps(json_data).encode('utf-8')
       headers = headers or {}
       headers['Content-Type'] = 'application/json'