##### 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

```

'''
        Load an image from a .tar archive
        :return: image dict
        '''
        try:
            self.log("Opening image %s" % self.load_path)
            image_tar = open(self.load_path, 'rb')
        except Exception as exc:
            self.fail("Error opening image %s - %s" % (self.load_path, str(exc)))
        try:
            self.log("Loading image from %s" % self.load_path)
            self.client.load_image(image_tar)
        except Exception as exc:
            self.fail("Error loading image %s - %s" % (self.name, str(exc)))
        try:
            image_tar.close()
        except Exception as exc:
            self.fail("Error closing image %s - %s" % (self.name, str(exc)))
        return self.client.find_image(self.name, self.tag)
def main():