Right now in the Ubuntu 14.04 base image for Docker the file
/etc/apt/preferences.d/ubuntu-esm-infra-trusty doesn't exist.
Subsequently, apt-get update enables ESM, but since we don't have a license to
use that upgrades / installs from ESM fail.
This workaround simply ensure that there is such a file pinning ESM to never be
used. With that, the creation of our image should succeed again.
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
