**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
Iterable,
    List,
    Optional,
    Set,
    Tuple,
    Type,
    Union,
    cast,
)
import jinja2
import pendulum
from croniter import croniter
from dateutil.relativedelta import relativedelta
from sqlalchemy import Boolean, Column, ForeignKey, Index, Integer, String, Text, func, or_
from sqlalchemy.orm import backref, joinedload, relationship
from sqlalchemy.orm.session import Session
from airflow import settings, utils
from airflow.configuration import conf
from airflow.exceptions import AirflowException, DuplicateTaskIdFound, TaskNotFound
from airflow.models.base import ID_LEN, Base
from airflow.models.baseoperator import BaseOperator
from airflow.models.dagbag import DagBag
from airflow.models.dagcode import DagCode
from airflow.models.dagparam import DagParam
from airflow.models.dagpickle import DagPickle
from airflow.models.dagrun import DagRun
from airflow.models.taskinstance import Context, TaskInstance, clear_task_instances
from airflow.security import permissions
from airflow.stats import Stats
from airflow.utils import timezone