Enable security in Update.1 builds

[Marco Pesenti Gritti]

Hello,

we need to enable security in the Update.1 images, since the plan is
to ship with it enabled. Looks like it's turned off in pilgrim at the
moment.

463  echo "  - turning off security by default"
464  rm -f $INSTALL_ROOT/etc/olpc-security

Dennis, we are planning to request approval for a few more packages
this afternoon, it would be good to make a new build with all of this
in.

Marco