Add an improved Docker file for CI.

tools/Dockerfile

+FROM ubuntu:20.04
+
+LABEL maintainer="Kim Nguyen <kim.nguyen@universite-paris-saclay.fr>"
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+ARG ocaml_version="4.12.0"
+ARG packages=""
+
+RUN apt-get update -y && \
+ apt-get dist-upgrade -y && \
+ apt-get install -y -q \
+ locales tzdata ca-certificates sudo ssh git \
+         autoconf automake autopoint autotools-dev binutils binutils-common \
+         binutils-dev binutils-x86-64-linux-gnu bsdmainutils build-essential \
+         cpp cpp-9 dwz g++ g++-9 gcc gcc-9 gcc-9-base gettext gettext-base \
+         groff-base intltool-debian libarchive-zip-perl libasan5 libatomic1 \
+         libbinutils libc-dev-bin libc6-dev libcc1-0 libcroco3 libcrypt-dev \
+         libctf-nobfd0 libctf0 libdebhelper-perl libdpkg-perl libelf1 \
+         libfile-stripnondeterminism-perl libgcc-9-dev libgomp1 libiberty-dev\
+         libisl22 libitm1 liblsan0 libmpc3 libmpfr6 libncurses-dev \
+         libncurses5-dev libpipeline1 libpthread-stubs0-dev libquadmath0 \
+         libsigsegv2 libstdc++-9-dev libsub-override-perl libtool libtsan0 libubsan1\
+         libuchardet0 libx11-dev libxau-dev libxcb1-dev libxdmcp-dev \
+         linux-libc-dev m4 make man-db pkg-config po-debconf x11proto-core-dev \
+         x11proto-dev libcurl4-gnutls-dev libexpat1-dev pkg-config wget unzip \
+         bubblewrap
+
+RUN mkdir -p /usr/local/bin && wget -O /usr/local/bin/opam \
+            'https://github.com/ocaml/opam/releases/download/2.0.8/opam-2.0.8-x86_64-linux' && \
+             chmod 755 /usr/local/bin/opam
+
+RUN echo "Europe/Paris" > /etc/timezone && \
+     ln -nsf /usr/share/zoneinfo/Europe/Paris /etc/localtime && \
+     sed -i -e 's/# en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen && \
+     locale-gen
+
+RUN adduser --disabled-password --gecos "" --shell /bin/bash cduce
+
+USER cduce
+
+ARG OPAMYES=true
+
+RUN opam init  --disable-sandboxing && \
+    opam switch create ${ocaml_version} && \
+    eval `opam config env` && \
+    test "${packages}" && opam install -y ${packages}
+
+ENV TZ "Europe/Paris"
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US:en
+ENV LC_ALL en_US.UTF-8
+ENV HOME /home/cduce
+
+ENTRYPOINT [ "opam", "exec", "--" ]
+
+CMD [ "/bin/sh", "-c", "bash" ]
\ No newline at end of file