**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. 

airflow/models/dag.py
session.query(DagRun.dag_id, func.count('*'))
            .filter(
                DagRun.dag_id.in_(existing_dag_ids),
                DagRun.state == State.RUNNING,  
                DagRun.external_trigger.is_(False),
            )
            .group_by(DagRun.dag_id)
            .all()
        )
        for orm_dag in sorted(orm_dags, key=lambda d: d.dag_id):
            dag = dag_by_ids[orm_dag.dag_id]
            if dag.is_subdag:
                orm_dag.is_subdag = True
                orm_dag.fileloc = dag.parent_dag.fileloc  
                orm_dag.root_dag_id = dag.parent_dag.dag_id  
                orm_dag.owners = dag.parent_dag.owner  
            else:
                orm_dag.is_subdag = False
                orm_dag.fileloc = dag.fileloc
                orm_dag.owners = dag.owner
            orm_dag.is_active = True
            orm_dag.last_parsed_time = timezone.utcnow()
            orm_dag.default_view = dag.default_view
            orm_dag.description = dag.description
            orm_dag.schedule_interval = dag.schedule_interval
            orm_dag.concurrency = dag.concurrency
            orm_dag.has_task_concurrency_limits = any(t.task_concurrency is not None for t in dag.tasks)
            orm_dag.calculate_dagrun_date_fields(
                dag,
                most_recent_dag_runs.get(dag.dag_id),