Error message handling incorrectly accesses error response title

[Michael Durrant]

barbicanclient/client.py - function _get_error_message lines 107-113:

def _get_error_message(self, resp):
    try:
        response_data = resp.json()
        message = response_data['title']
    except ValueError:
        message = resp.content
    return message

It appears response_data does not always contain a "title" attribute - but if response_data contains an "error" attribute, "error" usually has a title hanging off of it. I express this in uncertain terms as there are probably thousands of potential methods that access this.

I believe the fix is:
  If response_data has an "error" attribute and the "error" attribute has a "title", return "title" as the error message, else return the response content.

I was able to reproduce the error by using the barbican_client_manager in neutron_lbaas and passing "check_only=False" to the get_cert method.