dBus backend spins the event loop

The Service Framework backend in waitForData() does:

QEventLoop loop;
loop.exec();

This isn't acceptable for Qt. This forces all code and libraries using SFW to be re-entrant and to expect the event loop to be spun at any time. This is not acceptable and not compatible with QML/v8.

This code must be changed to block properly and only process SFW events while waiting. An example can be taken from the Unix backend on how to handle this issue.