Fix overcloud node delete after an upgrade

In fbc435ce16, we stopped passing
'parameters' to stack update call. This is backward incompatible
as the 'parameters' set for the stack before an upgrade would take
precedence over the ones set in 'parameter_defaults' of plan env.

Change-Id: Ia1d823386da687154c433136bf22ae6a0291573d
Closes-Bug: #1749636

tripleo_common/actions/scale.py

@@ -83,6 +83,11 @@ class ScaleDownAction(templates.ProcessTemplatesAction):
         fields = processed_data.copy()
         fields['timeout_mins'] = timeout_mins
         fields['existing'] = True
+        # As we do a PATCH update when deleting nodes, parameters set for a
+        # stack before upgrade to newton (ex. ComputeRemovalPolicies),
+        # would still take precedence over the ones set in parameter_defaults
+        # after upgrade. Clear these parameters for backward compatibility.
+        fields['clear_parameters'] = list(parameters.keys())
 
         LOG.debug('stack update params: %s', fields)
         self.get_orchestration_client(context).stacks.update(self.container,

tripleo_common/tests/actions/test_scale.py

@@ -139,14 +139,12 @@ class ScaleDownActionTest(base.TestCase):
             template={'heat_template_version': '2016-04-30'}
         )
 
-        heatclient.stacks.update.assert_called_once_with(
-            'stack',
-            stack_name='stack',
-            template={'heat_template_version': '2016-04-30'},
-            environment=env,
-            existing=True,
-            files={},
-            timeout_mins=240)
+        clear_list = list(['ComputeCount', 'ComputeRemovalPolicies'])
+        _, kwargs = heatclient.stacks.update.call_args
+        self.assertEqual(set(kwargs['clear_parameters']), set(clear_list))
+        self.assertEqual(kwargs['environment'], env)
+        self.assertEqual(kwargs['existing'], True)
+        self.assertEqual(kwargs['files'], {})
 
         mock_cache.assert_called_with(
             mock_ctx,