Fix VM base images being overwritten

The base image is used as backing image for the VM images, so
overwriting it results in corrupt data after VM reboots.

site-cookbooks/kosmos_kvm/attributes/default.rb

@@ -0,0 +1,7 @@
+ubuntu_server_cloud_image_release = "20220530"
+
+node.default["kosmos_kvm"]["host"]["qemu_base_image"] = {
+  "url" => "https://cloud-images.ubuntu.com/releases/focal/release-#{ubuntu_server_cloud_image_release}/ubuntu-20.04-server-cloudimg-amd64-disk-kvm.img",
+  "checksum" => "0295bee0539924774327d5267aa8e2eeac315b9efea7136c83643fce454529b8",
+  "path" => "/var/lib/libvirt/images/base/ubuntu-20.04-server-cloudimg-amd64-disk-kvm-#{ubuntu_server_cloud_image_release}.qcow2"
+}

site-cookbooks/kosmos_kvm/recipes/host.rb

@@ -12,17 +12,19 @@ directory "/var/lib/libvirt/images/base" do
   mode "0750"
 end
 
-# Base Ubuntu 20.04 image
-remote_file "/var/lib/libvirt/images/base/ubuntu-20.04-server-cloudimg-amd64-disk-kvm.qcow2" do
-  source "http://cloud-images.ubuntu.com/releases/focal/release/ubuntu-20.04-server-cloudimg-amd64-disk-kvm.img"
+# Base VM image
+remote_file node["kosmos_kvm"]["host"]["qemu_base_image"]["path"] do
+  source node["kosmos_kvm"]["host"]["qemu_base_image"]["url"]
+  checksum node["kosmos_kvm"]["host"]["qemu_base_image"]["checksum"]
   owner "libvirt-qemu"
   group "kvm"
   mode "0640"
 end
 
-cookbook_file "/usr/local/sbin/create_vm" do
-  source "create_vm"
+template "/usr/local/sbin/create_vm" do
+  source "create_vm.erb"
   mode "0750"
+  variables base_image_path: node["kosmos_kvm"]["host"]["qemu_base_image"]["path"]
 end
 
 firewall_rule 'ssh-alt-port' do

site-cookbooks/kosmos_kvm/templates/create_vm.erb

@@ -16,10 +16,9 @@ DISKSIZE=${4:-10} # 10GB default
 
 # Directory where image files will be stored
 IMAGE_DIR=/var/lib/libvirt/images
-IMAGE_FILE=${VMNAME}.qcow2
-IMAGE_PATH=$IMAGE_DIR/$IMAGE_FILE
+IMAGE_PATH=$IMAGE_DIR/${VMNAME}.qcow2
 CIDATA_PATH=${IMAGE_DIR}/cidata-${VMNAME}.iso
-BASE_FILE=${IMAGE_DIR}/base/ubuntu-20.04-server-cloudimg-amd64-disk-kvm.qcow2
+BASE_FILE=<%= @base_image_path %>
 
 # Create the VM image if it does not already exist
 if [ ! -f "$IMAGE_PATH" ]; then