guestfs: fix virt-resize failure for custom images

The virt-resize command was failing because it requires a pre-allocated
output file with the target size, not an empty temporary file.

Fix by:
1. Pre-allocating the temporary image file with qemu-img create before
   running virt-resize
2. Adding -f raw flag to qemu-img resize to avoid format detection
   warnings

This ensures the partition expansion works correctly when resizing
custom images like Debian 13 daily builds.

Error was:
  virt-resize: error: /tmp/ansible.depq5vk0.raw: file is too small to
  be a disk image (0 bytes)

Generated-by: Claude AI
Signed-off-by: Luis Chamberlain <[email protected]>

Author: mcgrof

playbooks/roles/base_image/tasks/custom-image.yml

@@ -50,7 +50,7 @@
   become: true
   become_method: ansible.builtin.sudo
   ansible.builtin.command:
-    cmd: "qemu-img resize {{ custom_image }} {{ libvirt_image_size }}"
+    cmd: "qemu-img resize -f raw {{ custom_image }} {{ libvirt_image_size }}"
   changed_when: true
   when:
     - custom_image_download is changed
@@ -65,6 +65,17 @@
     - custom_image_download is changed
     - guestfs_has_custom_raw_image_url|bool
 
+- name: Pre-allocate space for the resized image
+  become: true
+  become_method: ansible.builtin.sudo
+  ansible.builtin.command:
+    cmd: "qemu-img create -f raw {{ temp_resized_image.path }} {{ libvirt_image_size }}"
+  changed_when: true
+  when:
+    - custom_image_download is changed
+    - guestfs_has_custom_raw_image_url|bool
+    - temp_resized_image.path is defined
+
 - name: Expand root partition to use full disk
   become: true
   become_method: ansible.builtin.sudo