restapi: add use_latest_template_version to vm restapi

Add the new optional parameter that is relevant for stateless vm creation.
It can be also passed when updating a vm.
By using it, users can select to always create stateless vm based on its
latest version of the used template.

Feature page
http://www.ovirt.org/Features/Template_Versions#REST_API

Change-Id: I38b569f7ef6df4d485dac15b804427c8248ab540
Signed-off-by: Alissa Bonas <abonas@redhat.com>