docker_swarm: hopefully fix debug CI problems, and fix check mode (#52825)

* Let's see some debug output.

* Also check LocalNodeState.

* Improve tests.

* Actually implement check mode.

* Add changelog.

* Add pretty-printing and more output.

test/integration/targets/docker_config/tasks/test_docker_config.yml

@@ -1,10 +1,14 @@
 ---
 - block:
+  - shell: "docker info --format '{% raw %}{{json .}}{% endraw %}' | python -m json.tool"
+
   - name: Make sure we're not already using Docker swarm
     docker_swarm:
       state: absent
       force: true
 
+  - shell: "docker info --format '{% raw %}{{json .}}{% endraw %}' | python -m json.tool"
+
   - name: Create a Swarm cluster
     docker_swarm:
       state: present