debian: fix interface file templating

Make it work for base Debian and Proxmox installs.

roles/debian/tasks/main.yml

@@ -42,19 +42,22 @@
       - vim
       - tmux
 
-# we don’t want to template this file because it gets overwritten by proxmox
-# so just try removing anything that messes with our definitions in interfaces.d
+# for base Debian the main interfaces file is just an include
 - name: Remove interface definitions added by installer
-  lineinfile:
-    path: /etc/network/interfaces
-    regexp: '^iface [^ ]* inet'
-    state: absent
+  when: not is_proxmox
+  copy:
+    dest: /etc/network/interfaces
+    content: 'source /etc/network/interfaces.d/*'
   notify: reload interfaces
 
+# for Proxmox the main interfaces file will define bridges
+# here we just remove the vmbr0 definition created by installer to preserve idempotency
 - name: Include interfaces.d definitions
+  when: is_proxmox
   lineinfile:
     path: /etc/network/interfaces
-    line: 'source /etc/network/interfaces.d/*'
+    regexp: '^(auto vmbr0|iface vmbr0|\t)' # our definitions start with four spaces instead of tab
+    state: absent
   notify: reload interfaces
 
 - name: Set up interfaces
@@ -121,5 +124,3 @@
         name: sshd@mgmt
         enabled: yes
       notify: reboot
-
-    - meta: flush_handlers