Add default value for 'interval' in dbunloader
Add default value for 'interval' in dbunloader

- Add default value for 'interval' in dbunloader as it is a new option so
  it may not be in the config file.

tofu-rocketry/apel,tofu-rocketry/apel,apel/apel,stfc/apel,apel/apel,stfc/apel