**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
"""Returns a boolean indicating whether this DAG is paused"""
        qry = session.query(DagModel).filter(DagModel.dag_id == self.dag_id)
        return qry.value(DagModel.is_paused)
    @property
    def is_paused(self):
        """This attribute is deprecated. Please use `airflow.models.DAG.get_is_paused` method."""
        warnings.warn(
            "This attribute is deprecated. Please use `airflow.models.DAG.get_is_paused` method.",
            DeprecationWarning,
            stacklevel=2,
        )
        return self.get_is_paused()
    @property
    def normalized_schedule_interval(self) -> Optional[ScheduleInterval]:
        """
        Returns Normalized Schedule Interval. This is used internally by the Scheduler to
        schedule DAGs.
        1. Converts Cron Preset to a Cron Expression (e.g ``@monthly`` to ``0 0 1 * *``)
        2. If Schedule Interval is "@once" return "None"
        3. If not (1) or (2) returns schedule_interval
        """
        if isinstance(self.schedule_interval, str) and self.schedule_interval in cron_presets:
            _schedule_interval = cron_presets.get(self.schedule_interval)  
        elif self.schedule_interval == '@once':
            _schedule_interval = None
        else:
            _schedule_interval = self.schedule_interval
        return _schedule_interval
    @provide_session
    def handle_callback(self, dagrun, success=True, reason=None, session=None):