Get the absolute path to the database configuration file.

def get_database_config_file():
    """Get the absolute path to the database configuration file."""
    cfg = get_project_configuration()
    if 'dbconfig' in cfg:
        if os.path.isfile(cfg['dbconfig']):
            return cfg['dbconfig']
        else:
            logging.info("File '%s' was not found. Adjust 'dbconfig' in your "
                         "~/.hwrtrc file.",
                         cfg['dbconfig'])
    else:
        logging.info("No database connection file found. "
                     "Specify 'dbconfig' in your ~/.hwrtrc file.")
    return None