RFR: 8219686: jdk/jfr/event/runtime/TestShutdownEvent.java recording file length is 0

[Erik Gahlin]

Hi,

Could I have a review of this test fix that retries 3 times when 
verifying the shutdown event from a crashed JVM.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8219686

Webrev:
http://cr.openjdk.java.net/~egahlin/8219686/

Testing:
test/jdk/jdk/jfr/event/runtime/TestShutdownEvent.java 100 times

Thanks
Erik