Improve and fix tests (#36)

* Parameterize test images.

* Use different images, similar to ansible/ansible#72698.

tests/integration/targets/docker_container_info/tasks/main.yml

@@ -29,7 +29,7 @@
   - name: Make sure container exists
     docker_container:
       name: "{{ cname }}"
-      image: alpine:3.8
+      image: "{{ docker_test_image_alpine }}"
       command: '/bin/sh -c "sleep 10m"'
       state: started
       force_kill: yes