Modify AsyncOpAbstract._wait_for_async_op and
IWD.wait_for_object_condition to call context.iteration() in the
blocking mode instead of calling context.pending() every 0.01s. This
gets rid of busy-waiting and also ensures that the condition is checked
after every single dbus (or other) event. This way a condition that
potentially occurs for less than 0.01s can be reliably waited for.