Correct provider default inheritance

We were inheriting the base section of a provider twice, which is
noticeable in the case of lists since they are appended.  This
change corrects that by starting with an empty dictionary.

Change-Id: Iedd54ee817c6bcd6dd32cdf34eb9ba73519eeb57

tests/fixtures/layouts/nodepool-defaults.yaml

@@ -43,6 +43,8 @@
       key-name: zuul
       volume-type: gp3
       volume-size: 10  # winner (all)
+      security-group-ids:
+        - sg1
     image-defaults:
       volume-size: 20
       iops: 20

tests/unit/test_configloader.py

@@ -1491,6 +1491,7 @@ class TestNodepoolConfig(LauncherBaseTestCase):
         self.assertEqual('debian-normal', label.name)
         self.assertEqual('debian', label.image)
         self.assertEqual('normal', label.flavor)
+
         label = layout.labels['debian-large']
         self.assertEqual('debian-large', label.name)
         self.assertEqual('debian', label.image)
@@ -1523,6 +1524,7 @@ class TestNodepoolConfig(LauncherBaseTestCase):
         self.assertEqual(900, label.max_ready_age)
         self.assertEqual('required', label.imds_http_tokens)
         self.assertFalse(label.host_key_checking)
+        self.assertEqual(['sg1'], label.security_group_ids)
 
         label = provider.labels['debian-large']
         self.assertEqual('gp3', label.volume_type)
@@ -1532,6 +1534,7 @@ class TestNodepoolConfig(LauncherBaseTestCase):
         self.assertEqual(300, label.max_ready_age)
         self.assertEqual('required', label.imds_http_tokens)
         self.assertFalse(label.host_key_checking)
+        self.assertEqual(['sg1'], label.security_group_ids)
 
         label = provider.labels['debian-local-normal']
         self.assertEqual('gp3', label.volume_type)
@@ -1541,6 +1544,7 @@ class TestNodepoolConfig(LauncherBaseTestCase):
         self.assertEqual(900, label.max_ready_age)
         self.assertEqual('required', label.imds_http_tokens)
         self.assertFalse(label.host_key_checking)
+        self.assertEqual(['sg1'], label.security_group_ids)
 
     @simple_layout('layouts/nodepool-defaults-redefinition.yaml',
                    enable_nodepool=True)

zuul/model.py

@@ -2029,8 +2029,7 @@ class ProviderConfig(ConfigObject):
             previous_section = parent_section
         inheritance_path.reverse()
 
-        root = inheritance_path[0]
-        config = copy.deepcopy(root.config)
+        config = {}
         connection = connections.get(connection_name)
         if connection is None:
             raise UnknownConnection(connection_name)