Update teardown docs

docs/troubleshooting.md

@@ -259,8 +259,8 @@ Lets take it as an example how to debug the root cause.
 
 If ever things fail beyond possible recovery, here's how to completely purge an OAS installation in order to start from scratch:
 
-    cluster$ systemctl stop k3s
+    cluster$ /usr/local/bin/k3s-killall.sh
     cluster$ systemctl disable k3s
-    cluster$ mount | egrep '(kubelet|nsfs|k3s)' | cut -d' ' -f 3 | xargs -n 1 umount
+    cluster$ mount | egrep '(kubelet|nsfs|k3s)' | cut -d' ' -f 3 | xargs --no-run-if-empty -n 1 umount
     cluster$ rm -rf /var/lib/{rancher,OpenAppStack,kubelet,cni,docker,etcd} /etc/{kubernetes,rancher} /var/log/{OpenAppStack,containers,pods} /tmp/k3s /etc/systemd/system/k3s.service
     cluster$ systemctl reboot