disable unattended-upgrades for images

Change-Id: Idc4bd64f14046150307746e619d88df079ab95af
diff --git a/debian-8/http/preseed.cfg b/debian-8/http/preseed.cfg
index b49b671..9c13ce1 100644
--- a/debian-8/http/preseed.cfg
+++ b/debian-8/http/preseed.cfg
@@ -38,7 +38,7 @@
 
 d-i pkgsel/include string openssh-server
 d-i pkgsel/install-language-support boolean false
-d-i pkgsel/update-policy select unattended-upgrades
+d-i pkgsel/update-policy select none
 popularity-contest popularity-contest/participate boolean false
 
 d-i pkgsel/upgrade select none