Correct authentication and token generation v3 api

1. Remove a wrong route mapper for '/v3/tokens' path.
2. Correct NOAUTH list to include path of authentication and token
generation v3 api.
3. Correct authentication implementation of the api.
Yep, pls refer https://github.com/openstack/python-keystoneclient/blob/master/keystoneclient/auth/identity/v3.py#L236