debian: improve proxmox detection

Assume non-proxmox debians don’t have /etc/pve so we don’t have to
depend on NetBox data.

roles/debian/tasks/main.yml

@@ -1,3 +1,11 @@
+- block:
+    - name: Determine if this is a Proxmox host
+      stat:
+        path: /etc/pve
+      register: stat_pve
+    - set_fact:
+        is_proxmox: "{{ stat_pve.stat.exists and stat_pve.stat.isdir }}"
+
 - name: Configure MOTD
   template:
     dest: /etc/motd
@@ -77,7 +85,7 @@
 
 - name: Set up firewall
   include_tasks: firewall.yml
-  when: is_virtual or cluster_type != 'proxmox' # proxmox has its own firewall configuration
+  when: not is_proxmox # proxmox has its own firewall configuration
 
 - name: Install automatic upgrade package
   package: