Allow login url to be specified in cc

Explanation: the UAA used to do everything, then we broke
out authentication into the Login Server quite some time ago.
For backwards compatibility we kept it in the UAA, but we
need to retire that feature.  And the cloud controller needs
to point at the Login Server (if there is one) for anything
that needs user authentication (including vmc).
Add boolean login_enabled to check for existence of login server
Add default value for uaa.no_ssl property.