RFR(XS): 8220352: Crash with assert(external_guard || result != __null) failed: Invalid JNI handle

[Chris Plummer]

Hi,

Please review the following:
https://bugs.openjdk.java.net/browse/JDK-8220352
http://cr.openjdk.java.net/~cjplummer/8220352/webrev.00/

The possible use of an invalid jni handle is being avoided by not 
deleting the globalrefs as the test exits. This is the same fix that was 
applied to JDK-8172995 when the same situation turned up there.

Before the fix I was able to reproduce the issue after 700 runs. I did 
1100 after the fix and did not see any problems.

thanks,

Chris