Unable to delete multi value records in Route53

## Summary

LibCloud is currently unable to delete multi-value DNS records (e.g. MX) in Route53. The earliest I've traced this problem back to is 2015, and while there have been several PR's (https://github.com/apache/libcloud/pull/988 and https://github.com/apache/libcloud/pull/432) to attempt to fix it, they've all been abandoned and not yet merged into master.

## Detailed Information

* LibCloud Version: 3.6.1
* Create multi-value MX record in Route53 zone
* Call delete_record()
* View LibCloud error:

`RecordDoesNotExistError: , record_id=MX:testrecord, value=>`

Inizia da Route53DNSDriver.delete_record() e riproduci il problema segnalato creando un record MX multi-valore, quindi chiamando delete_record(). Leggi le PR #988 e #432 per conoscere i precedenti approcci tentati. Il lavoro è completato quando i record Route53 multi-valore possono essere eliminati senza il RecordDoesNotExistError segnalato.

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