**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
"""Upgrade the database."""
    
    from alembic import command
    log.info("Creating tables")
    config = _get_alembic_config()
    config.set_main_option('sqlalchemy.url', settings.SQL_ALCHEMY_CONN.replace('%', '%%'))
    
    errs = auto_migrations_available()
    if errs:
        for err in errs:
            log.error("Automatic migration is not available\n%s", err)
        return
    command.upgrade(config, 'heads')
    add_default_pool_if_not_exists()
def resetdb():
    """Clear out the database"""
    log.info("Dropping tables that exist")
    connection = settings.engine.connect()
    drop_airflow_models(connection)
    drop_flask_models(connection)
    initdb()
def drop_airflow_models(connection):