Added test - to check content host names are unique

please review it 
thanks
From this until the end is better to do like the following

```python
wit with self.assertRaises(CLIFactoryError):
    make_content_host({
        u'name': name,
        u'organization-id': self.NEW_ORG['id'],
        u'content-view-id': self.DEFAULT_CV['id'],
        u'lifecycle-environment-id': self.LIBRARY['id'],
    })
```

I have just realized this, sorry.