Installation or upgrade of 16.2.6 is timing out without any errors

Issue

• Installation or upgrade of 16.2.6 is timing out without any errors and in /var/log/containers/mistral/engine.log we see the following traceback:

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/mistral/engine/task_handler.py", line 113, in _on_action_complete
    task.on_action_complete(action_ex)
  File "/usr/lib/python3.6/site-packages/osprofiler/profiler.py", line 160, in wrapper
    result = f(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/mistral/engine/tasks.py", line 493, in on_action_complete
    self.complete(state, state_info)
  File "/usr/lib/python3.6/site-packages/osprofiler/profiler.py", line 160, in wrapper
    result = f(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/mistral/engine/tasks.py", line 279, in complete
    data_flow.publish_variables(self.task_ex, self.task_spec)
  File "/usr/lib/python3.6/site-packages/mistral/workflow/data_flow.py", line 219, in publish_variables
    task_ex.published = expr.evaluate_recursively(branch_vars, expr_ctx)
  File "/usr/lib/python3.6/site-packages/mistral/expressions/__init__.py", line 100, in evaluate_recursively
    data[key] = _evaluate_item(data[key], context)
  File "/usr/lib/python3.6/site-packages/mistral/expressions/__init__.py", line 79, in _evaluate_item
    return evaluate(item, context)
  File "/usr/lib/python3.6/site-packages/mistral/expressions/__init__.py", line 71, in evaluate
    return evaluator.evaluate(expression, context)
  File "/usr/lib/python3.6/site-packages/mistral/expressions/yaql_expression.py", line 187, in evaluate
    data_context
  File "/usr/lib/python3.6/site-packages/mistral/expressions/yaql_expression.py", line 141, in evaluate
    ", data=%s]" % (expression, str(e), data_context)
mistral.exceptions.YaqlEvaluationException: Can not evaluate YAQL expression [expression="{0}-messages".format($.plan_name), error=No method "format" for receiver {0}-messages matches supplied arguments, data={'__task_execution': {'id': '92d741d6-6395-40c9-ab94-57a2dab9a7bc', 'name': 'prepare_messages'}, 'payload': {'status': 'SUCCESS', 'message': ['overcloud'], 'root_execution_id': None, 'execution_id': '37605ebc-0d1c-4719-ac8d-8b7abcd45a17', 'plan_name': None, 'deployment_status': None, 'plans': ['overcloud']}, '__env': {}, 'openstack': {'user': '[...]