Add "real" Vagrant format options to image building.
    
    We originally added Vagrant support by tweaking options sent
    to the existing RHEV-M and vSphere OVA generation code.  This was
    a bit of a hack and resulted in confusing filenames.
    
    This adds "vagrant-libvirt" and "vagrant-virtualbox" image types,
    passes in the correct options to Image Factory and produces output
    files with the conventional ".box" extension and more descriptive
    and less confusing vagrant name suffixes.