object_storage.get_object doesn't retrieve the contents

[TAKAHASHI Yuto]

Both of `object_store.get_object` and `object_store.get_object_metadata` return only the metadata of objects.

Assume the pre-condition:

```
$ openstack object list test-container
+-------------+
| Name |
+-------------+
| sample.json |
+-------------+
```

Execute the script:

```
#!/usr/bin/env python
# -*- coding: utf-8 -*-

from openstack import connection

if __name__ == "__main__":
    conn = connection.from_config("my-cloud")
    res1 = conn.object_store.get_object(
            obj="sample.json",
            container="test-container"
    )
    res2 = conn.object_store.get_object_metadata(
            obj="sample.json",
            container="test-container"
    )
    print(res1)
    print(res2)
    print(res1 == res2)
```

Then the result is:

```
$ ./main.py
openstack.object_store.v1.obj.Object(content-type=application/json, content-length=43, etag=80ab0a2947eed0f35cf187281a2c50b5, accept-ranges=bytes, container=test-container, x-timestamp=1517899240.42680, last-modified=Tue, 06 Feb 2018 06:40:41 GMT, id=sample.json)
openstack.object_store.v1.obj.Object(content-type=application/json, content-length=43, etag=80ab0a2947eed0f35cf187281a2c50b5, accept-ranges=bytes, container=test-container, x-timestamp=1517899240.42680, last-modified=Tue, 06 Feb 2018 06:40:41 GMT, id=sample.json)
True
```

It shows that `get_object` and `get_object_metadata` return the same results.