Add simple playbook task for upgrading servers

We want to treat our servers as cattle; hopefully when this is fleshed out a bit more, it can accomplish the job without too many casualties.

playbooks/tasks/upgrade-servers.yml

@@ -9,6 +9,8 @@
       pacman:
         update_cache: yes
         upgrade: yes
+      register: pacman_upgrade
 
     - name: reboot
       reboot:
+      when: pacman_upgrade.changed