**Description**
The documentation and the error message of the [check-migrations](https://airflow.apache.org/docs/apache-airflow/stable/cli-and-env-variables-ref.html#check-migrations) / `def check_migrations` could be more verbose.  This check can fail if the underlying database was never initialised.


**Use case / motivation**

We are deploying our airflow helm chart with terraform helm provider. This provider has a [bug](https://github.com/hashicorp/terraform-provider-helm/issues/683) with helm hook. If airflow would give us a bit more verbose error message why could the `check-migrations` fail, we would find the underlying error/bug much sooner.


**Are you willing to submit a PR?**
Yes



airflow/utils/db.py
"""
    Drops all Flask models.
    :param connection: SQLAlchemy Connection
    :return: None
    """
    from flask_appbuilder.models.sqla import Base
    Base.metadata.drop_all(connection)  
@provide_session
def check(session=None):
    """
    Checks if the database works.
    :param session: session of the sqlalchemy
    """
    session.execute('select 1 as is_alive;')
    log.info("Connection successful.")