The azureml.net and azureml-int.net API returns different body content and error codes

[andrie]

Some (undocumented) changes in the AzureML API causes the same function call to return different results in PROD and INT.

For example, in INT, the response still contains error codes in the response body, but often this body is no longer JSON encoded, but plain text.

This means:

• In try_fetch() and validate_response() we have to handle both cases
• We have to handle both cases in some of the unit tests, especially to see if the function returns helpful error messages.