**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. 

tests/models/test_dag.py
"""
        Test that when 'params' is _not_ passed to a new Dag, that the params
        attribute is set to an empty dictionary.
        """
        dag = models.DAG('test-dag')
        assert isinstance(dag.params, dict)
        assert 0 == len(dag.params)
    def test_params_passed_and_params_in_default_args_no_override(self):
        """
        Test that when 'params' exists as a key passed to the default_args dict
        in addition to params being passed explicitly as an argument to the
        dag, that the 'params' key of the default_args dict is merged with the
        dict of the params argument.
        """
        params1 = {'parameter1': 1}
        params2 = {'parameter2': 2}
        dag = models.DAG('test-dag', default_args={'params': params1}, params=params2)
        params_combined = params1.copy()
        params_combined.update(params2)
        assert params_combined == dag.params
    def test_dag_invalid_default_view(self):
        """
        Test invalid `default_view` of DAG initialization
        """
        with pytest.raises(AirflowException, match='Invalid values of dag.default_view: only support'):
            models.DAG(dag_id='test-invalid-default_view', default_view='airflow')
    def test_dag_default_view_default_value(self):