**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("test_schedule_interval", schedule_interval=schedule_interval)
        assert dag.normalized_schedule_interval == expected_n_schedule_interval
        assert dag.schedule_interval == schedule_interval
    def test_set_dag_runs_state(self):
        clear_db_runs()
        dag_id = "test_set_dag_runs_state"
        dag = DAG(dag_id=dag_id)
        for i in range(3):
            dag.create_dagrun(run_id=f"test{i}", state=State.RUNNING)
        dag.set_dag_runs_state(state=State.NONE)
        drs = DagRun.find(dag_id=dag_id)
        assert len(drs) == 3
        assert all(dr.state == State.NONE for dr in drs)
    def test_create_dagrun_run_id_is_generated(self):
        dag = DAG(dag_id="run_id_is_generated")
        dr = dag.create_dagrun(run_type=DagRunType.MANUAL, execution_date=DEFAULT_DATE, state=State.NONE)
        assert dr.run_id == f"manual__{DEFAULT_DATE.isoformat()}"
    def test_create_dagrun_run_type_is_obtained_from_run_id(self):
        dag = DAG(dag_id="run_type_is_obtained_from_run_id")
        dr = dag.create_dagrun(run_id="scheduled__", state=State.NONE)
        assert dr.run_type == DagRunType.SCHEDULED
        dr = dag.create_dagrun(run_id="custom_is_set_to_manual", state=State.NONE)
        assert dr.run_type == DagRunType.MANUAL
    def test_create_dagrun_job_id_is_set(self):