Possible error in godaddy & hostvirtual DNS RECORD_TYPE_MAP

## Summary

[libcloud/dns/drivers/hostvirtual.py](libcloud/dns/drivers/hostvirtual.py#L65) and [libcloud/dns/drivers/godaddy.py](libcloud/dns/drivers/godaddy.py#L111) both contain the following definition:

```
RECORD_TYPE_MAP = {
RecordType.A: 'A',
RecordType.AAAA: 'AAAA',
RecordType.CNAME: 'CNAME',
RecordType.MX: 'MX',
RecordType.NS: 'SPF',
RecordType.SRV: 'SRV',
RecordType.TXT: 'TXT',
}
```

The line `RecordType.NS: 'SPF',` is very unusual. I suspect this is a bug. This is only two of three places in the libcloud/driver library where there is a mismatch between record type and name. (The other is in cloudflare.py, which defines `RecordType.URL: 'LOC'`).

If it is really not a bug, I suggest to add a comment explaining this mismatch.

My apologies for not adding a full bug report with reproducible code. I encountered this during a coarse check which record types are commonly supported.

Inizia con le definizioni di RECORD_TYPE_MAP in libcloud/dns/drivers/hostvirtual.py#L65 e libcloud/dns/drivers/godaddy.py#L111. Confronta la gestione dei record NS e SPF da parte delle API dei provider, quindi esamina i test corrispondenti del driver DNS, se disponibili. Il lavoro è completato quando confermi che il mapping è corretto oppure lo correggi, aggiungendo un commento che spieghi la discrepanza se è intenzionale.

Scritto dal modello di indicizzazione a partire dal testo della issue.