core: use template version on add vm/pool

When adding a stateless vm, or vm-pool,
if using the latest version of a template, we need to get latest version available and use
it.
http://www.ovirt.org/index.php?title=Features/Template_Versions

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1037478

Change-Id: I2d1b3ee9cd64d73866762fbf5fe02a468cdd578e
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>