patch to properly handle phone_home option

as per my conversation with juan, i m sending this patch to properly handle phone_home option, by including it within the first files section at the end of the XML we pass when starting with cloudinit.
i ve also doublechecked that the resulting user_data payload is correctly handled by cloudinit ( despite having several runcmd sections).

Note i ve also maintained for backward compatibility additional fileslist section though they will be ignored for ovirt > 3.3 as per https://bugzilla.redhat.com/show_bug.cgi?id=1138564 ( closed as NOTABUG)