Comment 7 for bug 1073241

forcing propagate can make sure def setup(product_name): work as it name hints.
After this function is called, our logger which are sub loggers of product_name should log as this function sets.

If we don't force it and any other third party codes have another handlers settings, such as stdout stream, all the loggers in our product will print the logs on stdout besides the handlers set up in this function.

Is my observation right?