Build of docker build images is erroring because of openjdk8

The build of our docker build images is erroring since few weeks because of a change on a parent image: apparently the Debian version has been upgraded and OpenJDK8 is not available anymore through apt:

The command '/bin/sh -c apt-get update && apt-get -y install openjdk-8-jdk openjdk-8-jre-headless' returned a non-zero code: 100

But the base jenkins/ssh-slave image already installs an AdoptOpenJDK Java8 image, so we should rely on it.