Protect against endpoint_data not existing

It's possible in get_api_major_version that the endpoint in question is
not found at all. In that case, we are documented to return None, but
what we do instead is throw an exception trying to get data off of the
None object.

Change-Id: I06ad497854f4e95a1a2a4a93241b244fc476b139

keystoneauth1/plugin.py

@@ -149,7 +149,9 @@ class BaseAuthPlugin(object):
         endpoint_data = self.get_endpoint_data(
             session, endpoint_override=endpoint_override,
             discover_versions=False, **kwargs)
-        return endpoint_data.api_version
+        if endpoint_data:
+            return endpoint_data.api_version
+        return None
 
     def get_endpoint(self, session, **kwargs):
         """Return an endpoint for the client.

keystoneauth1/tests/unit/test_discovery.py

@@ -560,6 +560,29 @@ class VersionDataTests(utils.TestCase):
 
         self.assertTrue(mock.called_once)
 
+    def test_version_data_legacy_ironic_no_override(self):
+        """Validate detection of legacy Ironic microversion ranges."""
+        ironic_url = 'https://bare-metal.example.com/v1/'
+        self.requests_mock.get(
+            ironic_url, status_code=200,
+            json={
+                'id': 'v1',
+                'links': [{
+                    "href": ironic_url,
+                    "rel": "self"}]},
+            headers={
+                'X-OpenStack-Ironic-API-Minimum-Version': '1.3',
+                'X-OpenStack-Ironic-API-Maximum-Version': '1.21',
+            })
+
+        plugin = noauth.NoAuth()
+        a = adapter.Adapter(
+            self.session,
+            auth=plugin,
+            service_type='baremetal')
+
+        self.assertIsNone(a.get_api_major_version())
+
     def test_version_data_ironic_microversions(self):
         """Validate detection of Ironic microversion ranges."""
         ironic_url = 'https://bare-metal.example.com/v1/'