Use the task loop to calculate multiple delegated hosts

Due to the way we're now calculating delegate_to, if that value is based
on a loop variable ('item') we need to calculate all of the possible
delegated_to variables for that loop.

Fixes #12499

test/units/vars/test_variable_manager.py

@@ -171,6 +171,7 @@ class TestVariableManager(unittest.TestCase):
 
         mock_task = MagicMock()
         mock_task._role = None
+        mock_task.loop = None
         mock_task.get_vars.return_value = dict(foo="bar")
 
         v = VariableManager()