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
diff --git a/tests/compat-in-docker.sh b/tests/compat-in-docker.sh
new file mode 100755
index 0000000..bbb860a
--- /dev/null
+++ b/tests/compat-in-docker.sh
@@ -0,0 +1,52 @@
+#!/bin/bash -eu
+
+# compat-in-docker.sh
+#
+# This file is part of mbed TLS (https://tls.mbed.org)
+#
+# Copyright (c) 2019, ARM Limited, All Rights Reserved
+#
+# Purpose
+# -------
+# This runs compat.sh in a Docker container.
+#
+# Notes for users
+# ---------------
+# If OPENSSL_CMD, GNUTLS_CLI, or GNUTLS_SERV are specified the path must
+# correspond to an executable inside the Docker container. The special
+# values "next" (OpenSSL only) and "legacy" are also allowed as shorthand
+# for the installations inside the container.
+#
+# See also:
+# - scripts/docker_env.sh for general Docker prerequisites and other information.
+# - compat.sh for notes about invocation of that script.
+
+source tests/scripts/docker_env.sh
+
+case "${OPENSSL_CMD:-default}" in
+    "legacy")  export OPENSSL_CMD="/usr/local/openssl-1.0.1j/bin/openssl";;
+    "next")    export OPENSSL_CMD="/usr/local/openssl-1.1.1a/bin/openssl";;
+    *) ;;
+esac
+
+case "${GNUTLS_CLI:-default}" in
+    "legacy")  export GNUTLS_CLI="/usr/local/gnutls-3.3.8/bin/gnutls-cli";;
+    "next")  export GNUTLS_CLI="/usr/local/gnutls-3.6.5/bin/gnutls-cli";;
+    *) ;;
+esac
+
+case "${GNUTLS_SERV:-default}" in
+    "legacy")  export GNUTLS_SERV="/usr/local/gnutls-3.3.8/bin/gnutls-serv";;
+    "next")  export GNUTLS_SERV="/usr/local/gnutls-3.6.5/bin/gnutls-serv";;
+    *) ;;
+esac
+
+run_in_docker \
+    -e M_CLI \
+    -e M_SRV \
+    -e GNUTLS_CLI \
+    -e GNUTLS_SERV \
+    -e OPENSSL_CMD \
+    -e OSSL_NO_DTLS \
+    tests/compat.sh \
+    $@