Implement keymgr list() method

Castellan KeyManager has added an abstract list() method starting
in release 0.13.0. We are currently safe since upper constraints
cap it at 0.12.0, but we will want to raise those constraints
soon.

This method isn't actually used in the Cinder code, but since it's
an ABC abstract method we must implement it in our ConfKeyMgr. This
just adds a basic skeleton so we don't blow up on missing the method.

Change-Id: Ie2b2aef40b4de36d011c7efa0ab5af5c9581a63d
Closes-bug: #1715451

cinder/keymgr/conf_key_mgr.py

@@ -144,3 +144,19 @@ class ConfKeyManager(key_manager.KeyManager):
                 reason="cannot delete non-existent key")
 
         LOG.warning("Not deleting key %s", managed_object_id)
+
+    def list(self, context, object_type=None, metadata_only=False):
+        """Retrieves a list of managed objects that match the criteria.
+
+        Note: Required abstract method starting with Castellan 0.13.0
+
+        :param context: Contains information of the user and the environment
+                        for the request.
+        :param object_type: The type of object to retrieve.
+        :param metadata_only: Whether secret data should be included.
+        :raises NotAuthorized: If no user context.
+        """
+        if context is None:
+            raise exception.NotAuthorized()
+
+        return []

cinder/tests/unit/keymgr/test_conf_key_mgr.py

@@ -116,3 +116,11 @@ class ConfKeyManagerTestCase(test.TestCase):
 
     def test_get_unknown_key(self):
         self.assertRaises(KeyError, self.key_mgr.get, self.ctxt, None)
+
+    def test_list(self):
+        keys = self.key_mgr.list(self.ctxt)
+        self.assertEqual(0, len(keys))
+
+    def test_list_null_context(self):
+        self.assertRaises(exception.NotAuthorized,
+                          self.key_mgr.list, None)