**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
num_active_runs.get(dag.dag_id, 0),
            )
            for orm_tag in list(orm_dag.tags):
                if orm_tag.name not in orm_dag.tags:
                    session.delete(orm_tag)
                orm_dag.tags.remove(orm_tag)
            if dag.tags:
                orm_tag_names = [t.name for t in orm_dag.tags]
                for dag_tag in list(dag.tags):
                    if dag_tag not in orm_tag_names:
                        dag_tag_orm = DagTag(name=dag_tag, dag_id=dag.dag_id)
                        orm_dag.tags.append(dag_tag_orm)
                        session.add(dag_tag_orm)
        if settings.STORE_DAG_CODE:
            DagCode.bulk_sync_to_db([dag.fileloc for dag in orm_dags])
        
        
        session.flush()
        for dag in dags:
            cls.bulk_write_to_db(dag.subdags, session=session)
    @provide_session
    def sync_to_db(self, session=None):
        """
        Save attributes about this DAG to the DB. Note that this method
        can be called for both DAGs and SubDAGs. A SubDag is actually a
        SubDagOperator.
        :return: None
        """
        self.bulk_write_to_db([self], session)
    def get_default_view(self):