Show detail on API error

[alexntt]

On pepper/libpepper.py, we have:

        except (HTTPError, URLError) as exc:
            logger.debug('Error with request', exc_info=True)
...
            if status == 500:
                raise PepperException('Server error.')

Could the PepperException show some details on what's happened? I see that there's some debug information printed out, but ideally PepperException should provide more details to the caller.

[gtmanfred]

Yes, we should log the error message if the status is 500.