Shorten path for XDG_CONFIG_HOME and clean dir

In Linux socket paths are limited to 108 char length.
/var/tmp/vm/$UID/.config will be too long in some cases.
So we use /var/tmp/vm/$UID

/var/tmp/vm must be
- cleaned on startup
- created with sticky-bit (used by different users)

roles/lmn_vm/tasks/main.yml

@@ -144,7 +144,7 @@
   ansible.builtin.copy:
     dest: /etc/tmpfiles.d/clean-vm.conf
     content: |
-      R! /var/tmp/vm
+      D /var/tmp/vm 1777 root root -
 
 - name: Install squid
   apt: