tools/dbus-run-session: fix race between manual and automatically started dbus-daemon on Windows

dbus-run-session starts a dbus server before the actual test application. If the start of the server is delayed for any reason, the test application may start another server due to the autostart function of the dbus library and the problem described in the ticket may occur.

The problem is solved by an explicit feedback of the server to dbus-run-session by means of an event that the server has been started completely. The test application is started only after receiving the feedback.

fixes #297 (closed) blocks !51 (closed), !95 (merged), !156, !193 (merged), !194 (closed) depends on !217 (merged)