fr: allow to disable web sso

[okozachenko1203]

Context

Atmosphere provides web sso via keycloak out of the box by implementing IdP federation in openstack keystone. And it sets this sso as the first option for auth in Horizon GUI.
Some users want to disable this sso or remove it from Horizon Auth option list at least.

Solution

We can use keystone_domains variable to enable/disable web sso on Horizon and idp federation on Keystone roles.
But need some changes