This machine type comes from downstream ubuntu 15.10. Replace it with a
somewhat equivalent qemu-2.3 machine type as we do have test data for
that.

The change allows the CPU code to pick a proper default CPU in the
'-latest' cases.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>