git: openjdk/loom: fibers: Re-work serviceability/jvmti/vthread/VThreadEventTest/VThreadEventTest.java to avoid unreliable setup

[duke]

Changeset: fb58007a
Author:    Alan Bateman <alan.bateman at oracle.com>
Date:      2024-02-09 18:06:03 +0000
URL:       https://git.openjdk.org/loom/commit/fb58007aa8f69d72857bcbfc282859c7190c82b4

Re-work serviceability/jvmti/vthread/VThreadEventTest/VThreadEventTest.java to avoid unreliable setup

! make/test/JtregNativeHotspot.gmk
! test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/VThreadEventTest.java
! test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp