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/mirror-image/template.json b/mirror-image/template.json
index 1b0369c..5abc542 100644
--- a/mirror-image/template.json
+++ b/mirror-image/template.json
@@ -96,7 +96,8 @@
         "scripts/mirrors.sh",
         "scripts/security.sh",
         "scripts/info.sh",
-        "scripts/cleanup.sh"
+        "scripts/cleanup.sh",
+        "scripts/zerodisk.sh"
       ]
     },
     {