Refactor python tests to run against python3.9

* Introduce sub-package compat to meet packaging and import requirements
* Update documenation for running tests
* Add requirements.txt to improve IDE support

Signed-off-by: Jhon Honce <jhonce@redhat.com>

test/python/docker/compat/common.py

@@ -0,0 +1,23 @@
+from docker import DockerClient
+
+from test.python.docker.compat import constant
+
+
+def run_top_container(client: DockerClient):
+    c = client.containers.create(
+        constant.ALPINE, command="top", detach=True, tty=True, name="top"
+    )
+    c.start()
+    return c.id
+
+
+def remove_all_containers(client: DockerClient):
+    for ctnr in client.containers.list(all=True):
+        ctnr.remove(force=True)
+
+
+def remove_all_images(client: DockerClient):
+    for img in client.images.list():
+        # FIXME should DELETE /images accept the sha256: prefix?
+        id_ = img.id.removeprefix("sha256:")
+        client.images.remove(id_, force=True)