RFR(S): 8138798 - improve tests for HotSpotVMEventListener::notifyInstall

[Dmitrij Pochepko]

Hi,

please review fix for JDK-8138798 - improve tests for 
HotSpotVMEventListener::notifyInstall

A test was improved to include negative cases(verifying that no install 
events sent on failed install attempt). Also, a minor refactoring was 
applied.

CR: https://bugs.openjdk.java.net/browse/JDK-8138798
webrev: http://cr.openjdk.java.net/~dpochepk/8138798/webrev.01/

Thanks,
Dmitrij