ovirt: Filter everything which does not end in .iso
    
    oVirt REST API does not provide a way to know what is a valid ISO image
    which can be assigned to a running VM. I've seen floppy disk images
    (.vfd) in a domain, which is already filtered. Now I've seen an ISO
    domain with .qcow2 files in it, which can't be assigned to a VM either.
    This commit filters every file which does not have a .iso extension as
    it's unlikely to be possible to use it.
    
    Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
    Acked-by: Eduardo Lima (Etrunko) <etrunko@redhat.com>