Implement detection and fail upon mismatch between /etc/xinet.d/tftp setting and
what it should be on the target OS during ltsp-build-client.  F-8 was /tftpboot
while F-9 was /var/lib/tftp.  An upgrade from F-8 to F-9 will currently not
automatically change the tftpdir if the xinetd service had been activated due to
%config(noreplace), so the user must be warned if their system doesn't match
this expectation.