<!--- 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
<!--- Explain the problem briefly below -->
The module docker_login save the config.json with 644 permission instead of 600 (default by docker login command)
##### 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 2.8.3
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/gael/.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 = 2.7.12 (default, Dec  4 2017, 14:50:18) [GCC 5.4.0 20160609]
```

##### 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. -->
Ubuntu 18.04 server

##### 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: Log into private registry and force re-authorization
  docker_login:
    registry: "{{ registry_host }}"
    username: "{{ registry_user }}"
    password: "{{ vault_registry_password }}"
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
ll /root/.docker/config.json 
-rw------- 1 root root 181 Jan 10 10:53 /root/.docker/config.json

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
ll /root/.docker/config.json 
-rw-r--r-- 1 root root 181 Jan 10 10:53 /root/.docker/config.json
<!--- Paste verbatim command output between quotes -->
```paste below

```

#
#
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 respectively the
      credentials store associated to the registry. Adding the credentials to the config files resp. the credential
      store 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:
    description:
      - The registry URL.
    type: str
    default: "https://index.docker.io/v1/"
    aliases:
      - registry