Add sparse argument to DockerClient.containers.list().

Signed-off-by: Matthieu Nottale <matthieu.nottale@docker.com>

docker/models/containers.py

@@ -873,6 +873,9 @@ class ContainerCollection(Collection):
                     container. Give the container name or id.
                 - `since` (str): Only containers created after a particular
                     container. Give container name or id.
+            sparse (bool): Do not inspect containers. Returns partial
+                informations, but guaranteed not to block. Use reload() on
+                each container to get the full list of attributes.
 
                 A comprehensive list can be found in the documentation for
                 `docker ps