Add fix for DSA 4371-1 (apt vulnerability)

Debian announced yesterday an important security update for apt: https://lists.debian.org/debian-security-announce/2019/msg00010.html

In projects/debootstrap-image we are downloading an Ubuntu 18.04.1 image, and doing an apt-get update -y in it before installing some packages using an affected apt version.

To avoid this we could download updated apt packages and install them using dpkg -i.

We should also check if the use of debootstrap is affected by the issue.