It's boot.log in standalone/configuration/logging.properties. 

That was done on purpose -- the launch script sets the system property, so the default typically wouldn't matter. But if the property isn't set, that means the user is doing something unusual, and we don't know what they want. So we kept the value as it was in previous releases in the same major version.

In this domain case, we know we programatically set the system property. So we could remove the default altogether. Or make it server.log as a hint to the user as to what will happen. Or leave it as boot.log so it is consistent with standalone/configuration/logging.properties. I'm indifferent as to which. :)