Add an ubuntu xenial base

Signed-off-by: Konstantin Pavlov <thresh@videolan.org>

videolan-base/xenial/Dockerfile

+FROM ubuntu:xenial
+
+MAINTAINER VideoLAN roots <roots@videolan.org>
+
+RUN apt-get update && \
+    apt-get install -y openssh-server openjdk-8-jdk lftp ca-certificates && \
+    apt-get clean -y && rm -rf /var/lib/apt/lists/* && \
+    sed -i 's|session    required     pam_loginuid.so|session    optional     pam_loginuid.so|g' /etc/pam.d/sshd && \
+    mkdir -p /var/run/sshd && \
+    adduser --quiet jenkins && \
+    echo "jenkins:jenkins" | chpasswd

videolan-base/xenial/Makefile

+.PHONY: build
+
+build:
+	docker build -t videolan-base-xenial:latest .