RFR : 8196854 :TestFlushableGZIPOutputStream failing with IndexOutOfBoundsException

[Seán Coffey]

A jdk8u (and earlier) issue where some new/recent test code meant that 
IndexOutOfBoundsException could be thrown.

https://bugs.openjdk.java.net/browse/JDK-8196854
http://cr.openjdk.java.net/~coffeys/webrev.8196854/webrev/

The buf array was never required and I've verified that the original 
8189789 issue can still be reproduced with a buggy JDK.

-- 
Regards,
Sean.