<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
`docker_login` reports no change even though it logged out.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
`docker_login`

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.1
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/raphael/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/dist-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.15+ (default, Nov 27 2018, 23:36:35) [GCC 7.3.0]

```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->

Client: Ubuntu 18.04 LTS 4.18.0-24-generic, ansible 2.8.1
Server: RHE7 3.10.0-957.21.3.el7.x86_64


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- name: Pull some Docker images 
  block:
  - name: Log into Harbor (Docker registry)
    docker_login:
        registry: "{{docker_registry}}"
        username: "{{harbor_user}}"
        password: "{{harbor_password}}"
        reauthorize: yes
  - name: Pull Docker images
    loop:
      - "some_image"
      - "other_image"
    docker_image:
      name: "{{ item }}"
      state: present
      source: pull
  always:
    - name: Docker logout
      docker_login:
        registry: "{{docker_registry}}"
        state: absent
```

##### EXPECTED RESULTS

Task `Docker logout` should report changes.


##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below
TASK [gears : Log into Harbor (Docker registry)] 
<snip>
changed: [<snip>] => {
    "changed": true, 
    "invocation": {
        "module_args": {
            "api_version": "auto", 
            "ca_cert": null, 
            "client_cert": null, 
            "client_key": null, 
            "config_path": "/home/<snip>/.docker/config.json", 
            "debug": false, 
            "docker_host": "unix://var/run/docker.sock", 
            "email": null, 
            "password": "VALUE_SPECIFIED_IN_NO_LOG_PARAMETER", 
            "reauthorize": true, 
            "registry": "<snip>", 
            "registry_url": "<snip>, 
            "ssl_version": null, 
            "state": "present", 
            "timeout": 60, 
            "tls": false, 
            "tls_hostname": "localhost", 
            "username": "<snip>", 
            "validate_certs": false
        }
    }, 
    "login_result": {
        "IdentityToken": "", 
        "Status": "Login Succeeded"
    }
}

<snip>
TASK [gears : Pull Docker images]
ok:
<snip>

TASK [gears : Docker logout]
<snip>
ok: [<snip>] => {
    "changed": false, 
    "invocation": {
        "module_args": {
            "api_version": "auto", 
            "ca_cert": null, 
            "client_cert": null, 
            "client_key": null, 
            "config_path": "/home/<snip>/.docker/config.json", 
            "debug": false, 
            "docker_host": "unix://var/run/docker.sock", 
            "email": null, 
            "password": null, 
            "reauthorize": false, 
            "registry": "<snip>", 
            "registry_url": "<snip>", 
            "ssl_version": null, 
            "state": "absent", 
            "timeout": 60, 
            "tls": false, 
            "tls_hostname": "localhost", 
            "username": null, 
            "validate_certs": false
        }
    }, 
    "login_result": {}
}
```

But, on that host:

```
$ cat .docker/config.json | grep auth
	"auths": {}
```

When I remove the logout task, the login appears in that output. So logout _is_ effective. 
#
#
from __future__ import absolute_import, division, print_function
__metaclass__ = type
ANSIBLE_METADATA = {'metadata_version': '1.1',
                    'status': ['preview'],
                    'supported_by': 'community'}
DOCUMENTATION = '''
---
module: docker_login
short_description: Log into a Docker registry.
version_added: "2.0"
description:
    - Provides functionality similar to the "docker login" command.
    - Authenticate with a docker registry and add the credentials to your local Docker config file. Adding the
      credentials to the config files allows future connections to the registry using tools such as Ansible's Docker
      modules, the Docker CLI and Docker SDK for Python without needing to provide credentials.
    - Running in check mode will perform the authentication without updating the config file.
options:
  registry_url:
    required: False
    description:
      - The registry URL.
    type: str
    default: "https://index.docker.io/v1/"
    aliases:
      - registry