Upgrade nipap database schema

def _db_upgrade(self, db_name):
        """ Upgrade nipap database schema
        """
        current_db_version = self._get_db_version()
        self._execute(db_schema.functions)
        for i in range(current_db_version, nipap.__db_version__):
            self._logger.info("Upgrading DB schema:", i, "to", i+1)
            upgrade_sql = db_schema.upgrade[i-1] # 0 count on array
            self._execute(upgrade_sql % (db_name))
        self._execute(db_schema.triggers)