**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
self,
        date_last_automated_dagrun: Optional[pendulum.DateTime],
    ) -> Tuple[Optional[pendulum.DateTime], Optional[pendulum.DateTime]]:
        """
        Get information about the next DagRun of this dag after ``date_last_automated_dagrun`` -- the
        execution date, and the earliest it could be scheduled
        :param date_last_automated_dagrun: The max(execution_date) of existing
            "automated" DagRuns for this dag (scheduled or backfill, but not
            manual)
        """
        if (
            self.schedule_interval == "@once" and date_last_automated_dagrun
        ) or self.schedule_interval is None:
            
            return (None, None)
        next_execution_date = self.next_dagrun_after_date(date_last_automated_dagrun)
        if next_execution_date is None:
            return (None, None)
        if self.schedule_interval == "@once":
            
            return (next_execution_date, next_execution_date)
        return (next_execution_date, self.following_schedule(next_execution_date))
    def next_dagrun_after_date(self, date_last_automated_dagrun: Optional[pendulum.DateTime]):