varnish: test with systemd

varnish/.kitchen.yml

@@ -3,6 +3,9 @@ driver:
   name: docker
   privileged: true
   use_sudo: false
+  # important if you need to interact with systemd
+  # otherwise a barebone ssh server is the main process
+  run_command: /sbin/init
 
 provisioner:
   name: ansible_playbook