All supported qemu versions at this point support both 'qemu-xhci' and
'nec-xhci' controllers. To allow using real capabilities restructure the
tests so that we test both controllers explicitly as well as the
selection of the default model.
Also add a xml2xml test invocation of the unified test.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
