Adding NTP server test code

adding NTP server test code
The code here doesn't work for me, and the value1,2,3 thing irked me......
```python
vals = [sel.value(getattr(configuration.ntp_servers, "ntp_server_{}".format(idx))) == '' for idx in range(1,4)]
assert all(vals)
```

I like this better for several reasons 
1) we only iterate once, which is just nice
2) we don't have 3 variables hanging around which don't need to be there
3) I had to change to compare to '' and not None because a blank input does not return None if it's blank but an empty string.