Fix nsk/jdi/stop/stop001 for virtual threads and remove from problem list

nsk/jdi/stop/stop001 is problem listed due to JDK-7034630, but that issue doesn't seem to reproduce anymore. It's suspected that it was only an issue on Solaris. For this reason stop001 should be removed from the problem list. However, it will fail due to lacking virtual thread support, so this issue also needs to be fixed at the same time. The issue is that for virtual threads, after work for JDK-8306434 and JDK-8306471 is complete, the test needs to expect IllegalThreadStateException rather than the stop() call succeeding.