**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 airflow models.
    :param connection: SQLAlchemy Connection
    :return: None
    """
    from airflow.models.base import Base
    
    
    chart = Table('chart', Base.metadata)
    chart.drop(settings.engine, checkfirst=True)
    user = Table('user', Base.metadata)
    user.drop(settings.engine, checkfirst=True)
    users = Table('users', Base.metadata)
    users.drop(settings.engine, checkfirst=True)
    dag_stats = Table('dag_stats', Base.metadata)
    dag_stats.drop(settings.engine, checkfirst=True)
    Base.metadata.drop_all(connection)
    
    Base.metadata.remove(dag_stats)
    Base.metadata.remove(users)
    Base.metadata.remove(user)
    Base.metadata.remove(chart)
    
    from alembic.migration import MigrationContext  
    migration_ctx = MigrationContext.configure(connection)
    version = migration_ctx._version  
    if version.exists(connection):
        version.drop(connection)
def drop_flask_models(connection):