**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
with DAG("test_dag", start_date=DEFAULT_DATE) as dag:
            op1 = DummyOperator(task_id='t1')
            op2 = DummyOperator(task_id='t2')
            op3 = DummyOperator(task_id='t3')
            op1 >> op2
            op2 >> op3
        sub_dag = dag.sub_dag('t2', include_upstream=True, include_downstream=False)
        assert id(sub_dag.task_dict['t1'].downstream_list[0].dag) == id(sub_dag)
        
        assert 't3' not in sub_dag._task_group.used_group_ids
    def test_schedule_dag_no_previous_runs(self):
        """
        Tests scheduling a dag with no previous runs
        """
        dag_id = "test_schedule_dag_no_previous_runs"
        dag = DAG(dag_id=dag_id)
        dag.add_task(BaseOperator(task_id="faketastic", owner='Also fake', start_date=TEST_DATE))
        dag_run = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=TEST_DATE,
            state=State.RUNNING,
        )
        assert dag_run is not None
        assert dag.dag_id == dag_run.dag_id
        assert dag_run.run_id is not None
        assert '' != dag_run.run_id
        assert (