**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
return session.query(DagModel).filter(DagModel.dag_id == dag_id).first()
    @classmethod
    @provide_session
    def get_current(cls, dag_id, session=None):
        return session.query(cls).filter(cls.dag_id == dag_id).first()
    @provide_session
    def get_last_dagrun(self, session=None, include_externally_triggered=False):
        return get_last_dagrun(
            self.dag_id, session=session, include_externally_triggered=include_externally_triggered
        )
    @staticmethod
    @provide_session
    def get_paused_dag_ids(dag_ids: List[str], session: Session = None) -> Set[str]:
        """
        Given a list of dag_ids, get a set of Paused Dag Ids
        :param dag_ids: List of Dag ids
        :param session: ORM Session
        :return: Paused Dag_ids
        """
        paused_dag_ids = (
            session.query(DagModel.dag_id)
            .filter(DagModel.is_paused.is_(True))
            .filter(DagModel.dag_id.in_(dag_ids))
            .all()
        )
        paused_dag_ids = {paused_dag_id for paused_dag_id, in paused_dag_ids}
        return paused_dag_ids
    def get_default_view(self) -> str: