##### SUMMARY
docker_image module is missing etc_hosts parameter even if this is documented and accepted by docker.build() as  of https://docker-py.readthedocs.io/en/stable/images.html

The same argument is accepted by docker_run but the lack of support here prevents us from building images when extra_hosts is needed.

I mention that the only reason why I propose using `etc_hosts` is in order to keep it in sync with already existing implementation from `docker_container` module which accepts `etc_hosts` which is translated to `extra_hosts` on docker-python-api.

I would personally prefer to use the same names as docker-api but this would require changing docker_container too.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
docker_image

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible-devel
```

##### 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. -->


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

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

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

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->


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

<!--- Paste verbatim command output between quotes -->
```paste below

```

client.module.params['source'] = 'build'
        elif client.module.params['load_path']:
            client.module.params['source'] = 'load'
        else:
            client.module.params['source'] = 'pull'
        client.module.warn('The value of the "source" option was determined to be "%s". '
                           'Please set the "source" option explicitly. Autodetection will '
                           'be removed in Ansible 2.12.' % client.module.params['source'])
    if client.module.params['force']:
        client.module.params['force_source'] = True
        client.module.params['force_absent'] = True
        client.module.params['force_tag'] = True
        client.module.warn('The "force" option will be removed in Ansible 2.12. Please '
                           'use the "force_source", "force_absent" or "force_tag" option '
                           'instead, depending on what you want to force.')
    try:
        results = dict(
            changed=False,
            actions=[],
            image={}
        )
        ImageManager(client, results)
        client.module.exit_json(**results)
    except DockerException as e:
        client.fail('An unexpected docker error occurred: {0}'.format(e), exception=traceback.format_exc())
    except RequestException as e:
        client.fail('An unexpected requests error occurred when docker-py tried to talk to the docker daemon: {0}'.format(e), exception=traceback.format_exc())
if __name__ == '__main__':
    main()