Add docker connection tests (#37)

* Add docker connection tests.

* Make it easier to switch image.

tests/integration/targets/connection_docker/shutdown.yml

@@ -0,0 +1,15 @@
+---
+- hosts: localhost
+  connection: local
+  vars:
+    docker_skip_cleanup: yes
+
+  tasks:
+    - name: Remove docker packages
+      action: "{{ ansible_facts.pkg_mgr }}"
+      args:
+        name:
+          - docker
+          - docker-ce
+          - docker-ce-cli
+        state: absent