Use ftp.halifax mirror

fsmpi-base/Dockerfile

 ARG DEBIAN_RELEASE=stretch
 FROM debian:${DEBIAN_RELEASE}
+ARG DEBIAN_RELEASE
 ENV LANG C.UTF-8
+COPY ${DEBIAN_RELEASE}.list /etc/apt/sources.list
 RUN apt-get update && apt-get install -y locales && rm -rf /var/lib/apt/lists/* \
     && for lang in en_US de_DE; do localedef -i $lang -c -f UTF-8 -A /usr/share/locale/locale.alias $lang.UTF-8; done

fsmpi-base/buster.list

+deb http://ftp.halifax.rwth-aachen.de/debian buster main
+deb http://security.debian.org/debian-security buster/updates main
+deb http://ftp.halifax.rwth-aachen.de/debian buster-updates main

fsmpi-base/stretch.list

+deb http://ftp.halifax.rwth-aachen.de/debian stretch main
+deb http://security.debian.org/debian-security stretch/updates main
+deb http://ftp.halifax.rwth-aachen.de/debian stretch-updates main