Fix exception parsing when using WSME

Services that use WSME return errors using a json document that contains
'faultstring' in the root object instead of a dict within a dict.

Change-Id: I25d8c64860de7eafb8d543ebcb519fc9664d563e
Story: 2008381
Task: 41303

openstack/exceptions.py

@@ -211,6 +211,9 @@ def raise_from_response(response, error_message=None):
         try:
             content = response.json()
             messages = [_extract_message(obj) for obj in content.values()]
+            if not any(messages):
+                # Exception dict may be the root dict in projects that use WSME
+                messages = [_extract_message(content)]
             # Join all of the messages together nicely and filter out any
             # objects that don't have a "message" attr.
             details = '\n'.join(msg for msg in messages if msg)

openstack/tests/unit/test_exceptions.py

@@ -213,3 +213,21 @@ class TestRaiseFromResponse(base.TestCase):
         self.assertEqual(response.status_code, exc.status_code)
         self.assertEqual(self.message, exc.details)
         self.assertIn(self.message, str(exc))
+
+    def test_raise_wsme_format(self):
+        response = mock.Mock()
+        response.status_code = 404
+        response.headers = {
+            'content-type': 'application/json',
+        }
+        response.json.return_value = {
+            'faultstring': self.message,
+            'faultcode': 'Client',
+            'debuginfo': None,
+        }
+        exc = self.assertRaises(exceptions.NotFoundException,
+                                self._do_raise, response,
+                                error_message=self.message)
+        self.assertEqual(response.status_code, exc.status_code)
+        self.assertEqual(self.message, exc.details)
+        self.assertIn(self.message, str(exc))