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/include/upgrade-server.yml

@@ -18,6 +18,18 @@
     state: absent
   when: inventory_hostname == "gemini.archlinux.org"
 
+- name: check for running builds
+  block:
+    - name: list systemd-nspawn processes
+      command: pgrep -x systemd-nspawn
+      register: pgrep_systemd_nspawn
+      ignore_errors: true
+
+    - name: stop without rebooting
+      meta: end_host
+      when: pgrep_systemd_nspawn is succeeded
+  when: "'buildservers' in group_names"
+
 - name: reboot
   reboot:
   when: pacman_upgrade is changed