support/testing: add python-docker test

Python-docker needs a working docker setup to do anything useful, so add it
to the existing docker_compose (which tests docker and docker-compose)
rather than adding a completely new test.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Christian Stewart <christian@aperture.us>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/testing/tests/package/sample_python_docker.py

@@ -0,0 +1,12 @@
+import docker
+
+client = docker.from_env()
+info = client.info()
+images = client.images.list()
+
+assert len(images) > 0
+
+print('Version:', info['ServerVersion'])
+print('Images:')
+for i in images:
+    print(i.tags[0])