Fix exception messages

API errors are in the format:

```json
{
"code":401,
"error":"Not Authorized",
"description":"2017-10-06T08:57:02-04:00, Error ERCDPLTFRM-DNLKUPERR occurred when accessing https://gateway.watsonplatform.net/tone-analyzer/api/v3/tone?version=2017-10-06&sentences=1, Tran-Id: gateway-dp01-307987946 - Invalid UserId and/or Password. Please confirm that your credentials match the end-point you are trying to access. A common error is trying to use credentials from an experimental or beta release against a GA release or vice versa"
}
```

We need to amend `\IBM\Watson\Common\Api\AbstractApi::handleErrors()` to account for that format.

Locate the PHP class containing IBM\Watson\Common\Api\AbstractApi::handleErrors() and inspect how it currently interprets API error responses. Use the JSON example in the issue as the reproduction input; done means the handler accounts for that response format without breaking existing error handling, with relevant tests if the repository provides them.

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