RFR: 8244291: Test: gc/z/TestGarbageCollectorMXBean.java failed: "unexpected cycles"

[Per Liden]

The test gc/z/TestGarbageCollectorMXBean.java has failed once on Windows 
(out of several thousands of runs) in our CI. I've been unable to 
reproduce the problem, and code inspection has not reviled anything 
suspicious. The only explanation that seems semi-plausible is that the 
the Notification thread was severely starved on CPU and didn't manage to 
send notifications in a timely manner.

This patch extends the notification timeout from 60 to 90 seconds, and 
adds additional logging with timestamps, which will hopefully help us 
understand the problem a bit better if it ever happens again.

Bug: https://bugs.openjdk.java.net/browse/JDK-8244291
Webrev: http://cr.openjdk.java.net/~pliden/8244291/webrev.0

/Per