[cfid-364] Make login server user remote auth endpoint.

The login server's RemoteUaaAuthenticationManager now calls
the uaa's RemoteAuthenticationEndpoint (at /authenticate) rather
than the standard UI endpoint. This is more robust than
relying on a redirect to detect successful authentication.

This will require a change to the login server's cf-release
template to the uaa.login.url property.

Change-Id: I07b6b437516eafc3241efefc018edbb8fa812b72