RFR: JDK-8275608: runtime/Metaspace/elastic/TestMetaspaceAllocationMT2 too slow [v4]

[Thomas Stuefe]

> Small tweaks to make these elastic metaspace stress tests faster.
> 
> Before, runtime for individual tests was wobbling between 40+ seconds and some rare timeouts at 3+ minutes, depending on machine load and random luck. Now, we get a steadfast 35-37 seconds.
> 
> I tested this manually, checking the numbers that we really test what we want to test (a lot of arena activity). Also GHAs and SAP nightlies.
> 
> Thanks, Thomas

Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - feedback alexey
 - Merge
 - Update test/hotspot/jtreg/runtime/Metaspace/elastic/RandomAllocator.java
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update test/hotspot/jtreg/runtime/Metaspace/elastic/RandomAllocator.java
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - adapt copyrights
 - tweaks to improve runtime

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6041/files
  - new: https://git.openjdk.java.net/jdk/pull/6041/files/7101f3df..c934a0c3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6041&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6041&range=02-03

  Stats: 29424 lines in 680 files changed: 24045 ins; 3070 del; 2309 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6041.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6041/head:pull/6041

PR: https://git.openjdk.java.net/jdk/pull/6041