Fix failing to parse json error msg

It assumes its a requests response but could
be a HTTPResponse from urllib.

Story: 2008789
Task: 42183

Change-Id: I7306d167a17284c7f478ec1c1599a8d4b32040c2
(cherry picked from commit f7551a6bac)
(cherry picked from commit 280acd2dff)

magnumclient/common/httpclient.py

@@ -69,6 +69,9 @@ def _extract_error_json(body, resp):
         try:
             body_json = resp.json()
             return _extract_error_json_text(body_json)
+        except AttributeError:
+            body_json = jsonutils.loads(body)
+            return _extract_error_json_text(body_json)
         except ValueError:
             return {}
     else: