The issue here is that keystoneauth usually treats all authentication methods the same, and uses them to authenticate and get another token. As you see the error in your log, trust scoped tokens can't create another token, so the authentication fails.

Some clients provide a mechanism for you to input the token and endpoint_url directly without requiring keystoneauth. See below and try that.

https://github.com/openstack/python-neutronclient/blob/master/neutronclient/client.py#L61-L62