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.

Beginne mit den RECORD_TYPE_MAP-Definitionen in libcloud/dns/drivers/hostvirtual.py#L65 und libcloud/dns/drivers/godaddy.py#L111. Vergleiche die Handhabung von NS- und SPF-Records durch die Provider-APIs und prüfe anschließend die entsprechenden DNS-Driver-Tests, sofern vorhanden. Erledigt bedeutet, zu bestätigen, dass das Mapping korrekt ist, oder es zu korrigieren und einen Kommentar hinzuzufügen, der die Abweichung erklärt, falls sie beabsichtigt ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.