Display error description

When an error happens, display both the title and the description of the
returned error if they exist, to give more context to the user.

Change-Id: I84457bfe2d55a877e72a7fcb6dd6ba54c557c45e
Closes-Bug: #1555102

barbicanclient/client.py

@@ -113,6 +113,9 @@ class _HTTPClient(adapter.Adapter):
         try:
             response_data = resp.json()
             message = response_data['title']
+            description = response_data.get('description')
+            if description:
+                message = '{0}: {1}'.format(message, description)
         except ValueError:
             message = resp.content
         return message

barbicanclient/tests/test_client.py

@@ -265,6 +265,13 @@ class WhenTestingGetErrorMessage(TestClient):
         msg = self.httpclient._get_error_message(resp)
         self.assertEqual(msg, content)
 
+    def test_gets_error_message_from_description_in_json(self):
+        resp = mock.MagicMock()
+        resp.json.return_value = {'title': 'test_text',
+                                  'description': 'oopsie'}
+        msg = self.httpclient._get_error_message(resp)
+        self.assertEqual(msg, 'test_text: oopsie')
+
 
 class BaseEntityResource(testtools.TestCase):