**Apache Airflow version**:
2.0.1

**Kubernetes version**:
Server Version: version.Info{Major:"1", Minor:"18+", GitVersion:"v1.18.9-eks-d1db3c", GitCommit:"d1db3c46e55f95d6a7d3e5578689371318f95ff9", GitTreeState:"clean", BuildDate:"2020-10-20T22:18:07Z", GoVersion:"go1.13.15", Compiler:"gc", Platform:"linux/amd64"}

**What happened**:
Clearing a failed subdag task with Downstream+Recursive does not automatically set the state of the parent dag to 'running' so that the downstream parent tasks can execute.

The work around is to manually set the state of the parent dag to running after clearing the subdag task

**What you expected to happen**:
With airflow version 1.10.4 the parent dag was automatically set to 'running' for this same scenario

**How to reproduce it**:
- Clear a failed subdag task selecting option for Downstream+Recursive
- See that all down stream tasks in the subdag as well as the parent dag have been cleared
- See that the parent dag is left in 'failed' state. 

tests/models/test_dag.py
"""Verify tasks with Duplicate task_id raises error"""
        with pytest.raises(DuplicateTaskIdFound, match="Task id 't1' has already been added to the DAG"):
            with DAG("test_dag", start_date=DEFAULT_DATE) as dag:
                op1 = DummyOperator(task_id="t1")
                op2 = BashOperator(task_id="t1", bash_command="sleep 1")
                op1 >> op2
        assert dag.task_dict == {op1.task_id: op1}
    def test_duplicate_task_ids_not_allowed_without_dag_context_manager(self):
        """Verify tasks with Duplicate task_id raises error"""
        with pytest.raises(DuplicateTaskIdFound, match="Task id 't1' has already been added to the DAG"):
            dag = DAG("test_dag", start_date=DEFAULT_DATE)
            op1 = DummyOperator(task_id="t1", dag=dag)
            op2 = DummyOperator(task_id="t1", dag=dag)
            op1 >> op2
        assert dag.task_dict == {op1.task_id: op1}
    def test_duplicate_task_ids_for_same_task_is_allowed(self):
        """Verify that same tasks with Duplicate task_id do not raise error"""
        with DAG("test_dag", start_date=DEFAULT_DATE) as dag:
            op1 = op2 = DummyOperator(task_id="t1")
            op3 = DummyOperator(task_id="t3")
            op1 >> op3
            op2 >> op3
        assert op1 == op2
        assert dag.task_dict == {op1.task_id: op1, op3.task_id: op3}
        assert dag.task_dict == {op2.task_id: op2, op3.task_id: op3}
    def test_sub_dag_updates_all_references_while_deepcopy(self):