RFR: 8225084: gc/z/TestHighUsage.java fails with unexpected allocation stall

[Per Liden]

After talking to Erik, I reworked the test to not depend on timing to 
avoid allocation stalls.

New webrev: http://cr.openjdk.java.net/~pliden/8225084/webrev.1

/Per

On 5/31/19 9:46 AM, Per Liden wrote:
> TestHighUsage might fail in case the test system is starved on CPU. This 
> patch adds a delay to allow for a GC cycle to complete even in those 
> situations. Also adding gc+start logging to allow for easier debugging 
> of test failures.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8225084
> Webrev: http://cr.openjdk.java.net/~pliden/8225084/webrev.0
> 
> /Per