installer: Actually reboot when the user presses "Reboot."

* gnu/installer/newt/final.scm (run-install-success-page): Return
'success.
* gnu/installer.scm (installer-program): Check the result of the 'final
step and reboot upon success.

gnu/installer.scm

@@ -314,6 +314,7 @@ (define installer-builder
                            guile-json guile-git guix)
       (with-imported-modules `(,@(source-module-closure
                                   `(,@modules
+                                    (gnu services herd)
                                     (guix build utils))
                                   #:select? module-to-import?)
                                ((guix config) => ,(make-config.scm)))
@@ -363,10 +364,20 @@ (define installer-builder
 
               (catch #t
                 (lambda ()
+                  (define results
                     (run-installer-steps
                      #:rewind-strategy 'menu
                      #:menu-proc (installer-menu-page current-installer)
                      #:steps steps))
+
+                  (match (result-step results 'final)
+                    ('success
+                     ;; We did it!  Let's reboot!
+                     (sync)
+                     (stop-service 'root))
+                    (_                            ;installation failed
+                     ;; TODO: Honor the result of 'run-install-failed-page'.
+                     #f)))
                 (const #f)
                 (lambda (key . args)
                   (let ((error-file "/tmp/last-installer-error"))

gnu/installer/newt/final.scm

@@ -56,7 +56,10 @@ (define (run-install-success-page)
    (G_ "Reboot")
    (G_ "Congratulations!  Installation is now complete.  \
 You may remove the device containing the installation image and \
-press the button to reboot.")))
+press the button to reboot."))
+
+  ;; Return success so that the installer happily reboots.
+  'success)
 
 (define (run-install-failed-page)
   (choice-window