##### 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

```

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##### 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

```

'''
        Build an image
        :return: image dict
        '''
        params = dict(
            path=self.build_path,
            tag=self.name,
            rm=self.rm,
            nocache=self.nocache,
            timeout=self.http_timeout,
            pull=self.pull,
            forcerm=self.rm,
            dockerfile=self.dockerfile,
            decode=True,
        )
        if self.client.docker_py_version < LooseVersion('3.0.0'):
            params['stream'] = True
        build_output = []
        if self.tag:
            params['tag'] = "%s:%s" % (self.name, self.tag)
        if self.container_limits:
            params['container_limits'] = self.container_limits
        if self.buildargs:
            for key, value in self.buildargs.items():
                self.buildargs[key] = to_native(value)
            params['buildargs'] = self.buildargs
        if self.cache_from: