core: query for getting 'updateable on next run' fields

Add query that gets two versions of VMs and returns the names of the
fields which are different between those versions and could be updated
only when the VM will be restarted.

Change-Id: I6fd7133770aafee5b2bc551d3cffc8951f5d58df
Signed-off-by: Arik Hadas <ahadas@redhat.com>