CloudDNSManager.get_record should probably return a CloudDNSRecord object

Currently CloudDNSManager.get_record returns a dict, it should probably return a CloudDNSRecord.

As it stands, if you get a record and then want to update it, you would have to do something like:

```python
record = domain.get_record(record_id)
record_obj = pyrax.clouddns.CloudDNSRecord(pyrax.cloud_dns, record, loaded=False)
domain.update_record(record_obj, data=data)
```

This is due to CloudDNSManager.update_record looking for record.name which expects record to be a CloudDNSRecord instance.

This modification would allow something such as:
```python
record = domain.get_record(record_id)
record.update(data=data)
```