Horizon can support several auth mechanisms, i.e. Keystone creds and
OpenID. User allowed to choose proper way of auth and disclaimer is
shown. But it is possible to allow choose from the only variant, and in
this case disclaimer also shown, which is confusing. Proposed patch fix
disclaimer display and makes it reasonable
Closes-bug: #1774623
Change-Id: Ib039c6fdf1e4cd21b5ebe426fe2a15355a37353c