Xenial Docker container has been added.

docker/xenial/Dockerfile

+FROM ubuntu:16.04
+MAINTAINER Mate Farkas <mate.farkas@sch.hu>
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get -y update && apt-get install -y \
+  openssh-server \
+  sudo \
+  vim
+
+RUN useradd -m -s /bin/bash vagrant
+ADD home/vagrant/.ssh/authorized_keys /home/vagrant/.ssh/authorized_keys
+RUN chmod 0700 /home/vagrant/.ssh/
+RUN chown -R vagrant. /home/vagrant/
+
+ADD etc/sudoers.d/vagrant /etc/sudoers.d/vagrant
+
+ADD root/bin/start_ssh /root/bin/start_ssh
+RUN chmod 0700 /root/bin/start_ssh
+
+EXPOSE 22
+CMD /root/bin/start_ssh
+

docker/xenial/Makefile

+TAG='matefarkas/xenial:base'
+
+all:
+	docker build --tag ${TAG} ${PWD}
+
+test:
+	docker run --interactive --tty --rm ${TAG} bash || true
+

docker/xenial/README.md

+# matefarkas/xenial:base
+
+Base image for Vagrant using Ubuntu 16.04 LTS (Xenial Xerus).
+

docker/xenial/etc/sudoers.d/vagrant

+vagrant ALL=(ALL) NOPASSWD: ALL
+

docker/xenial/home/vagrant/.ssh/authorized_keys

+ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6NF8iallvQVp22WDkTkyrtvp9eWW6A8YVr+kz4TjGYe7gHzIw+niNltGEFHzD8+v1I2YJ6oXevct1YeS0o9HZyN1Q9qgCgzUFtdOKLv6IedplqoPkcmF0aYet2PkEDo3MlTBckFXPITAMzF8dJSIFo9D8HfdOV0IAdx4O7PtixWKn5y2hMNG0zQPyUecp4pzC6kivAIhyfHilFR61RGL+GPXQ2MWZWFYbAGjyiYJnAmCP3NOTd0jMZEnDkbUvxhMmBYSdETk1rRgm+R4LOzFUGaHqHDLKLX+FIPKcF96hrucXzcWyLbIbEgE98OHlnVYCzRdK8jlqm8tehUc9c9WhQ== vagrant insecure public key
+

docker/xenial/root/bin/start_ssh

+#!/bin/bash
+
+mkdir -p /var/run/sshd
+/usr/sbin/sshd -D -f /etc/ssh/sshd_config
+