Adapt http response error message parsing

Due I05d2bb60b211d1b18611070217b01e3e418eb79a, change the error message
parsing to get error message from response.

Closes-Bug: #1555985
Change-Id: I4da3aff76fe46d1ac9fd90e06cb4931dc9a8d203
(cherry picked from commit e9c6c1a2a3)

magnumclient/common/httpclient.py

@@ -44,6 +44,12 @@ def _extract_error_json(body):
         if 'error_message' in body_json:
             raw_msg = body_json['error_message']
             error_json = json.loads(raw_msg)
+        else:
+            error_body = body_json['errors'][0]
+            raw_msg = error_body['title']
+            error_json = {'faultstring': error_body['title'],
+                          'debuginfo': error_body['detail']}
+
     except ValueError:
         return {}