Restore auth-less version negotiation
change Change-Id: I097bf70431a999a0f6aa56079ffb5743b50d4d7f
inadvertently started to require (keystone) authentication
when accessing API root to get the API version document.
This breaks standard version negotiation (that usually does not require
auth) and also some monitoring / loadbalancing that used to check
returns on GET to API root.