build: Assert successful completion of cloud-init

cloud-init/user-data.template

@@ -11,14 +11,14 @@ packages:
   - cifs-utils
 
 runcmd:
-  - apt-get install -y linux-modules-extra-$(uname -r)
+  - apt-get install -y --no-install-recommends linux-modules-extra-$(uname -r)
   - sysctl -w net.ipv6.conf.all.disable_ipv6=1
   - systemctl enable --now qemu-guest-agent.service
   - cloud-init clean --logs
   - truncate -s 0 /etc/hostname /etc/machine-id
   - rm -f /etc/ssh/ssh_host_* /var/lib/dbus/machine-id
   - ln -s /etc/machine-id /var/lib/dbus/machine-id
-  - poweroff
+  - echo "TEMPLATE_GENERATION_SUCCESS" | tee /var/log/template-generation-success
 
 disable_root: false
 users:
@@ -30,3 +30,8 @@ users:
       - ${PUBLIC_SSHKEY}
 ssh_authorized_keys:
   - ${PUBLIC_SSHKEY}
+
+power_state:
+  delay: now
+  mode: poweroff
+  condition: true