DBus: Generated interface code doesn't permit setting flags

Qt DBus's generated code doesn't allow setting the flags of DBus method calls: namely, autostart service, reply required, and interactive authorization allowed.
Some services require using the interactive authorization allowed flag for desired behaviour (e.g. Freedesktop Accounts Service), which means that the generated interface wrappers can't be used, and instead you need to use direct QDBusMessage and QDBusConnection invocations.