pdist-bootcheck: Use persistent directory as safeguard

The file that is supposed to prevent boot loops in case of pdist
failures is incorrectly created in a per-boot directory and is therefore
ineffective. Move the file fom /var/run to /var/cache.

pdist/pdist-bootcheck

@@ -30,17 +30,17 @@ if [ "$need_async_pdist" ]; then
         netcat $(distmaster) 237
     echo triggered background update
 elif [ "$need_pdist_and_reboot" ]; then
-    if [[ -e /var/run/updatecheck.reboot-triggered ]]; then
+    if [[ -e /var/cache/updatecheck.reboot-triggered ]]; then
         echo "Update and reboot required but prevented due to previous attempt"
-        rm /var/run/updatecheck.reboot-triggered
+        rm /var/cache/updatecheck.reboot-triggered
         exit 1
     fi
     if (( $(stat -f -c %f /) * $(stat -f -c %s /) /1024/1024/1024 < 10)); then
         echo "Update and reboot required but prevented because of insufficient free disk space (<10G)"
         exit 1
     fi
     echo "Update and reboot required"
-    touch /var/run/updatecheck.reboot-triggered
+    touch /var/cache/updatecheck.reboot-triggered
     sync /
     while true; do sleep 5; echo "System update in progress. Please be patient..."; done &
     netcat $(distmaster) 237