**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
assert op1.dag is dag
        assert op1.owner == 'owner1'
        assert op2.dag is dag2
        assert op2.owner == 'owner2'
        with dag2:
            op3 = DummyOperator(task_id='op3')
        assert op3.dag is dag2
        assert op3.owner == 'owner2'
        with dag:
            with dag2:
                op4 = DummyOperator(task_id='op4')
            op5 = DummyOperator(task_id='op5')
        assert op4.dag is dag2
        assert op5.dag is dag
        assert op4.owner == 'owner2'
        assert op5.owner == 'owner1'
        with DAG('creating_dag_in_cm', start_date=DEFAULT_DATE) as dag:
            DummyOperator(task_id='op6')
        assert dag.dag_id == 'creating_dag_in_cm'
        assert dag.tasks[0].task_id == 'op6'
        with dag:
            with dag:
                op7 = DummyOperator(task_id='op7')
            op8 = DummyOperator(task_id='op8')
        op9 = DummyOperator(task_id='op8')
        op9.dag = dag2
        assert op7.dag == dag
        assert op8.dag == dag
        assert op9.dag == dag2
    def test_dag_topological_sort_include_subdag_tasks(self):