Hide Java thread pools and executors impelementation details in the trace

[eupp]

Consider the following example:

val executorService = Executors.newFixedThreadPool(2)
val future = executorService.submit(task)
future.get()

Currently, if a lincheck test fails in such a case, it would also output in the trace all the implementation details of the executor service and thread pool classes. These details typically would not be relevant to the user (assuming bug occurs in user code, and not in the Java stdlib classes themself).

We need to improve on this, and do not show these details by default to the user.