Handle username for strongops command

Take username for authentication or new registrations.

Adjusted the error handling based on NodeFly/nodefly-registration now
always returning an error object for errors.

Changes messaging to communicate that the username is the login for
either strongloop.com or strongops.

*note* PR recreated by me so  that I can release master with loopback changes. We'll delay merge of this until just before release of SSO.