the build server builds your application in release mode, but logging is still enabled as that is useful for debugging on device.
As soon as you build your game for publishing to the App Stores, all log outputs are removed! Alex will write a blog post in the following days how to release games with the build server for the App stores and we will add a publishing guide with the next release.
In the next release, you can also set a new property
to whatever value you like and even change it at runtime. This information is added to http://doc.v-play.net/qml-components-system.html. You can then disable logging completely from QML for example for debug builds, or enable logging for release builds if you want to.
Until the next release, you do not need to bother about the log outputs, as they do not affect the performance that much, and the build server applications are release builds as mentioned earlier.