Remove deleted override vars from inventory

When re-running the dynamic_inventory.py script, either directly or via
a playbook run, deployers expect that their edits to
openstack_user_config.yml are reflected in the inventory. However, previous
behavior only added new entries or updated existing variables with new
values; variables that were deleted remained in the inventory JSON
file.

This patch only corrects behavior for the variables includes in the
global_overrides dictionary. Similar behavior may be present in other
aspects of the inventory, such as removing host vars, but those should
be addressed in later patches.

Closes-Bug: #1588902

Change-Id: I86d6627ef34d99c7ef3c77fcd42c918a13f0fe81

playbooks/inventory/dynamic_inventory.py

@@ -871,6 +871,11 @@ def _parse_global_variables(user_cidr, inventory, user_defined_config):
                 user_defined_config['global_overrides']
             )
 
+            # Remove global overrides that were deleted from inventory, too
+            for key in inventory['all']['vars'].keys():
+                if key not in user_defined_config['global_overrides']:
+                    del inventory['all']['vars'][key]
+
 
 def append_if(array, item):
     """Append an ``item`` to an ``array`` if its not already in it.

releasenotes/notes/remove-overrides-17ef7d0496f6a6c7.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - Deleting variable entries from the ``global_overrides`` dictionary in
+    ``openstack_user_config.yml`` now properly removes those variables from
+    the ``openstack_inventory.json`` file. See Bug #1588902.

tests/test_inventory.py

@@ -382,6 +382,12 @@ class TestConfigChecks(unittest.TestCase):
         with open(USER_CONFIG_FILE, 'wb') as f:
             f.write(yaml.dump(self.user_defined_config))
 
+    def restore_config(self):
+        # get back our initial user config file
+        os.remove(USER_CONFIG_FILE)
+        os.rename(USER_CONFIG_FILE + ".tmp", USER_CONFIG_FILE)
+        self.config_changed = False
+
     def test_missing_container_cidr_network(self):
         self.delete_provider_network('container')
         with self.assertRaises(SystemExit) as context:
@@ -519,9 +525,7 @@ class TestConfigChecks(unittest.TestCase):
 
     def tearDown(self):
         if self.config_changed:
-            # get back our initial user config file
-            os.remove(USER_CONFIG_FILE)
-            os.rename(USER_CONFIG_FILE + ".tmp", USER_CONFIG_FILE)
+            self.restore_config()
 
 
 class TestStaticRouteConfig(TestConfigChecks):
@@ -643,6 +647,45 @@ class TestNetAddressSearch(unittest.TestCase):
         self.assertEqual(pns, new_pns)
 
 
+class TestGlobalOverridesConfigDeletion(TestConfigChecks):
+    def setUp(self):
+        super(TestGlobalOverridesConfigDeletion, self).setUp()
+        self.inventory = get_inventory()
+
+    def add_global_override(self, var_name, var_value):
+        """Adds an arbitrary name and value to the global_overrides dict."""
+        overrides = self.user_defined_config['global_overrides']
+        overrides[var_name] = var_value
+
+    def remove_global_override(self, var_name):
+        """Removes target key from the global_overrides dict."""
+        overrides = self.user_defined_config['global_overrides']
+        del overrides[var_name]
+
+    def test_global_overrides_delete_when_merge(self):
+        """Vars removed from global overrides are removed from inventory"""
+        self.add_global_override('foo', 'bar')
+
+        di._parse_global_variables({}, self.inventory,
+                                   self.user_defined_config)
+
+        self.remove_global_override('foo')
+
+        di._parse_global_variables({}, self.inventory,
+                                   self.user_defined_config)
+
+        self.assertNotIn('foo', self.inventory['all']['vars'],
+                         "foo var not removed from group_vars_all")
+
+    def test_global_overrides_merge(self):
+        self.add_global_override('foo', 'bar')
+
+        di._parse_global_variables({}, self.inventory,
+                                   self.user_defined_config)
+
+        self.assertEqual('bar', self.inventory['all']['vars']['foo'])
+
+
 class TestMultipleRuns(unittest.TestCase):
     def test_creating_backup_file(self):
         inventory_file_path = os.path.join(TARGET_DIR,