Adds debug code to diagnose Issue#755

[ebozduman]

This is not a fix but debug code to add the following information to the log_output list to help diagnose the sporadic problem, explained in Issue #755.

log_output.args['presigned_get_object_url'] = presigned_get_object_url
log_output.args['response.status'] = response.status
log_output.args['response.reason'] = response.reason
log_output.args['response.headers'] = json.dumps(response.headers.__dict__)
log_output.args['response._body'] = response._body.decode('utf-8')

The suspicion is that the client and server times are not in sync and hence we sometimes see the problem when the expiration time is either comes earlier or later than expected.

[kannappanr]

LGTM