Support for using the persistent-auth

With persisted_auth set to true, we can by-pass the full ovirt authentication,
which can rapidly speed-up the response times
(at least when running against some external authentication).

In my setup, it is 4x faster with this feature turned on. For more details see
http://www.ovirt.org/Features/RESTSessionManagement.
do we need to add some ovirt version tests?