Docker modules: improve documentation on docker vs. docker-py Python package requirements (#42457)

* Make sure all docker-py/docker requirements are listed, and clarify about docker vs. docker-py.

* Adjusting changes made in #40839.

lib/ansible/modules/cloud/docker/docker_container.py

@@ -96,7 +96,6 @@ options:
     description:
       - Path to a file containing environment variables I(FOO=BAR).
       - If variable also present in C(env), then C(env) value will override.
-      - Requires docker >= 2.3.0.
   entrypoint:
     description:
       - Command that overwrites the default ENTRYPOINT of the image.
@@ -421,7 +420,13 @@ author:
 
 requirements:
     - "python >= 2.6"
-    - "docker >= 2.3.0"
+    - "docker-py >= 1.7.0"
+    - "Please note that the L(docker-py,https://pypi.org/project/docker-py/) Python
+       module has been superseded by L(docker,https://pypi.org/project/docker/)
+       (see L(here,https://github.com/docker/docker-py/issues/1310) for details).
+       For Python 2.6, C(docker-py) must be used. Otherwise, it is recommended to
+       install the C(docker) Python module. Note that both modules should I(not)
+       be installed at the same time."
     - "Docker API >= 1.20"
 '''
 
@@ -619,7 +624,7 @@ try:
         from docker.utils.types import Ulimit, LogConfig
     from ansible.module_utils.docker_common import docker_version
 except:
-    # missing docker handled in ansible.module_utils.docker
+    # missing docker-py handled in ansible.module_utils.docker
     pass
 
 
@@ -2016,7 +2021,8 @@ class AnsibleDockerClientContainer(AnsibleDockerClient):
 
         init_supported = init_supported and LooseVersion(docker_version) >= LooseVersion('2.2')
         if self.module.params.get("init") and not init_supported:
-            self.fail('docker-py version is %s. Minimum version required is 2.2 to set init option.' % (docker_version,))
+            self.fail("docker or docker-py version is %s. Minimum version required is 2.2 to set init option. "
+                      "If you use the 'docker-py' module, you have to switch to the docker 'Python' package." % (docker_version,))
 
         self.HAS_INIT_OPT = init_supported
         self.HAS_AUTO_REMOVE_OPT = HAS_DOCKER_PY_2 or HAS_DOCKER_PY_3