rootfs: fix lack of reboot after update

The problem is that the "reboot" command sends the signal to the init. However,
it looks like init queues all incoming signals. They're handled after all
"sysinit" commands from the inittab are finished.
reboot -f skip sending the signal and triggers the reboot immediately.

This problem pop up after update of a buildroot to version 2016.02.

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>

userspace/rootfs_override/etc/init.d/wrs-boot-procedure

@@ -201,11 +201,23 @@ if $change_update_date; then
 fi
 # If we changed bloader or kernel or initramfs, we reboot. Otherwise proceed.
 if $reboot; then
+    cd /
     umount /update
     umount /boot
+    echo "Gentle reboot"
     reboot
-    # We notified init, but it takes time. Stop breathing while waiting to die.
-    sleep 9999
+    sleep 2
+    # If init ignores signals before all sysinit entires from inittab are done,
+    # we have to force the reboot.
+    echo "Force reboot"
+    # Firstly, remount / in case we use nfs
+    /bin/mount -o remount,ro /
+    # umount what is left
+    /bin/umount -a -r
+    # force reboot
+    reboot -f
+    # wait forever
+    while true; do sleep 1; done
 fi
 
 # Here we are: boot normally: if initrd, mount /usr and copy /etc