[PLAT-6340] Fix CAsynchronousTest issues

Use a barrier instead of timeouts to align behaviour of the CAsynchronous instance and test thread.
Move the assertion out of CTestAsyncOperation3 to avoid mis-reporting on Windows builds.
Reviewed-by: Chris Kent
[PLAT-6340] Fix semaphore destruction issue from previous commit

The previous solution allows the notification semaphore to be destroyed prematurely. A reference counted form avoids this.
Reviewed-by: Stephen Colebourne
[DVI-315] Fix relative paths from pom

Reviewed-by: Stephen Colebourne