add default value for http_status in ClientException

ClientException is not a virtual base class, hence it can be
initialized and string formatted, but the required property
'http_status' is not set by defaut, which will cause AttributeError
if we cannot convert a dedicate exception from response.

This patch fixes it by adding default value 'N/A' for http_status,
and set it with response.status_code when it is a ClientException
instance.

Change-Id: Ib9920a1f21885917fe7bc4562f1b54602112a473
Closes-Bug: #1586994

aodhclient/exceptions.py

@@ -15,6 +15,7 @@
 class ClientException(Exception):
     """The base exception class for all exceptions this library raises."""
     message = 'Unknown Error'
+    http_status = 'N/A'
 
     def __init__(self, message=None, request_id=None,
                  url=None, method=None):
@@ -181,6 +182,10 @@ def from_response(response, url, method=None):
     elif content_type.startswith("text/"):
         kwargs['message'] = response.text
 
-    if not kwargs['message']:
+    if not kwargs.get('message'):
-        del kwargs['message']
+        kwargs.pop('message', None)
-    return cls(**kwargs)
+
+    exception = cls(**kwargs)
+    if isinstance(exception, ClientException) and response.status_code:
+        exception.http_status = response.status_code
+    return exception

aodhclient/tests/unit/test_exceptions.py

@@ -0,0 +1,37 @@
+# Copyright 2016 Hewlett Packard Enterprise Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import mock
+from oslotest import base
+
+from aodhclient import exceptions
+
+
+class AodhclientExceptionsTest(base.BaseTestCase):
+    def test_string_format_base_exception(self):
+        # ensure http_status has initial value N/A
+        self.assertEqual('Unknown Error (HTTP N/A)',
+                         '%s' % exceptions.ClientException())
+
+    def test_no_match_exception_from_response(self):
+        resp = mock.MagicMock(status_code=520)
+        resp.headers = {
+            'Content-Type': 'text/plain',
+            'x-openstack-request-id': 'fake-request-id'
+        }
+        resp.text = 'Of course I still love you'
+        e = exceptions.from_response(resp, 'http://no.where:2333/v2/alarms')
+        self.assertIsInstance(e, exceptions.ClientException)
+        self.assertEqual('Of course I still love you (HTTP 520) '
+                         '(Request-ID: fake-request-id)', '%s' % e)