core: use the right template on template version update

Move the setting of the template & template id that the VM is going to
switch-to in UpdateVmVersionCommand to the constructor.

Change-Id: I7dd3475b30267c918497e4971ebd1da1cfb6e58e
Bug-Url: https://bugzilla.redhat.com/1149135
Signed-off-by: Arik Hadas <ahadas@redhat.com>