Enable zerofree script

  * Warning:
    - mirror-image - it will require ~120Gb
    - day01 - it will require ~55Gb
    - ubuntu-16.04 - it will require ~10Gb
    from backend build system.
  * Those option decrease size, but significantly increases build time

Change-Id: Ib7ac5b0c4297e75c79d7d514a07b07104959145d
diff --git a/ubuntu-16.04/template.json b/ubuntu-16.04/template.json
index cfcb6f0..84e1a59 100644
--- a/ubuntu-16.04/template.json
+++ b/ubuntu-16.04/template.json
@@ -61,7 +61,8 @@
             "scripts/network.sh",
             "scripts/security.sh",
             "scripts/cleanup.sh",
-            "scripts/info.sh"
+            "scripts/info.sh",
+            "scripts/zerodisk.sh"
           ]
         },
         "openstack": {
@@ -72,7 +73,8 @@
             "scripts/network.sh",
             "scripts/security.sh",
             "scripts/cleanup.sh",
-            "scripts/info.sh"
+            "scripts/info.sh",
+            "scripts/zerodisk.sh"
           ]
         },
         "docker": {