client inadvertently encourages use of token/endpoint

Given the following args, the client asks for an endpoint instead of additional credentials (which is preferred):

    $ keystone --token=asdf --os-username=asdf token-get
    Expecting an endpoint provided via either --os-endpoint or env[OS_SERVICE_ENDPOINT]

As a result, users end up bypassing authentication and are more likely to run into issues not having a service catalog, etc.