mistral workflow create UnicodeEncodeError in python3

in python3, mistral workflow-create/update will raise UnicodeEncodeError if yaml cantains chinese.

# mistral workflow-update -f yaml gw_deploy/workflows/vm/tencent_cvm_create.yaml
ERROR (app) 'latin-1' codec can't encode characters in position 111-112: Body ('中文') is not valid Latin-1. Use body.encode('utf-8') if you want to send it encoded in UTF-8.