**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
dag = DAG(
            'dag',
            start_date=DEFAULT_DATE,
        )
        with dag:
            DummyOperator(task_id='task', owner='owner1')
            subdag = DAG(
                'dag.subtask',
                start_date=DEFAULT_DATE,
            )
            
            subdag.parent_dag = dag
            subdag.is_subdag = True
            SubDagOperator(task_id='subtask', owner='owner2', subdag=subdag)
        session = settings.Session()
        dag.sync_to_db(session=session)
        orm_dag = session.query(DagModel).filter(DagModel.dag_id == 'dag').one()
        assert set(orm_dag.owners.split(', ')) == {'owner1', 'owner2'}
        assert orm_dag.is_active
        assert orm_dag.default_view is not None
        assert orm_dag.default_view == conf.get('webserver', 'dag_default_view').lower()
        assert orm_dag.safe_dag_id == 'dag'
        orm_subdag = session.query(DagModel).filter(DagModel.dag_id == 'dag.subtask').one()
        assert set(orm_subdag.owners.split(', ')) == {'owner1', 'owner2'}
        assert orm_subdag.is_active
        assert orm_subdag.safe_dag_id == 'dag__dot__subtask'
        assert orm_subdag.fileloc == orm_dag.fileloc
        session.close()
    def test_sync_to_db_default_view(self):