Add proper qemu-caching for source image

  * Require command at slaves:
    'mkdir -p "${HOME}/packer_images_cache/"'
    since packer not able to do it.
  * set SALT_STOPSTART_WAIT=10 for salt bootstrap
  * Dd iptables to base installation

Change-Id: Icc5a50a21e848b93660aa80483b6fdd3e27de243
diff --git a/ubuntu-16.04/template.json.env b/ubuntu-16.04/template.json.env
index 12be33e..ed6351e 100644
--- a/ubuntu-16.04/template.json.env
+++ b/ubuntu-16.04/template.json.env
@@ -1,5 +1,7 @@
 # Env variables and description:
-DO_API_TOKEN
+#DO_API_TOKEN
+PACKER_IMAGES_CACHE="${HOME}/packer_images_cache/"
+
 
 # base.sh
 UBUNTU_BASEURL=http://mirror.mirantis.com/stable/ubuntu/