Test to check if the activation-key's content-host limit actually limits its usage

Hey now I get it, what @Ichimonji10  was suggesting.
Let's move it to robottelo/test.py under the `class UITestCase` and `def setUpClass`.

```python
def setUpClass(cls):
    cls.server_name = conf.properties['main.server.hostname']
```
This way we will be assigning the value to server_name just once for all of the UI.