RFR: 8218401: WRONG_PHASE: vmTestbase/nsk/jvmti test crash

[Daniil Titov]

Please review the change that fixes 3 tests that intermittently fail with JVMTI_ERROR_WRONG_PHASE error.

The problem here is that the callbacks these tests enable keep processing events and perform JVMTI calls after VM is terminated. The fix makes these test listen for VMDeath event and  quick return from the callbacks after VMDeath event is received.

Webrev: http://cr.openjdk.java.net/~dtitov/8218401/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8218401

Thanks!
-Daniil