Add docker-based test scripts

Enable running tests under Docker. This makes it easier to spin up an
environment with all dependencies (especially the multiple versions of
openssl and gnutls needed).
* tests/docker/xenial/Dockerfile: Definition for the docker image,
  including local builds for openssl and gnutls.
* tests/scripts/docker_env.sh: New helper script that creates the Docker
  image and has a function to run a command in the Docker container.
* tests/docker/all-in-docker.sh: Wrapper for all.sh under Docker.
* tests/docker/basic-in-docker.sh: Script that runs the same commands as
  .travis.yml, in Docker.
* tests/ssl-opt-in-docker.sh: Wrapper to run ssl-opt.sh in Docker.
* tests/compat-in-docker.sh: Wrapper to run compat.sh in Docker.
* tests/make-in-docker.sh: Wrapper to run make in Docker.

Change-Id: Ie092b1deed24c24c3859754535589523ce1d0a58

tests/scripts/all-in-docker.sh

@@ -0,0 +1,24 @@
+#!/bin/bash -eu
+
+# all-in-docker.sh
+#
+# This file is part of mbed TLS (https://tls.mbed.org)
+#
+# Copyright (c) 2018-2019, ARM Limited, All Rights Reserved
+#
+# Purpose
+# -------
+# This runs all.sh (except for armcc) in a Docker container.
+#
+# Notes for users
+# ---------------
+# See docker_env.sh for prerequisites and other information.
+#
+# See also all.sh for notes about invocation of that script.
+
+source tests/scripts/docker_env.sh
+
+# Run tests that are possible with openly available compilers
+run_in_docker tests/scripts/all.sh \
+    --no-armcc \
+    $@