Bug#183360: prebaseconfig: 'cancel' button do not cancel
At the end of prebaseconfig, the user is told that the machine will
now reboot from hard drive. When using DEBIAN_FRONTEND=slang, two
buttons appear, <next> and <cancel>. When pressing <cancel>, I expect
the installation to stop, and not reboot the machine. The current
implementation instead continues with the reboot, just as if I had
If the <cancel> button appear, it should work.