Removed references to tower in InventorySource and Credentials

--- Removed reference to tower in  InventorySource and InventoryUpdate model
--- Added a migration for above change
--- Added new CONTROLLER* variables in awx/main/models/credentials/__init__.py
--- Migrated awxkit to new CONTROLLER* variables
--- Updated the tests to use new CONTROLLER* variables
--- Fix some issues with upgrade path, rename more cases

awx/main/tests/functional/test_credential.py

@@ -101,6 +101,7 @@ def test_default_cred_types():
         'vault',
         'vmware',
     ]
+
     for type_ in CredentialType.defaults.values():
         assert type_().managed_by_tower is True