RFR: 8271722: [TESTBUG] gc/g1/TestMixedGCLiveThreshold.java can fail if G1 Full GC uses >1 workers [v3]

[Richard Reingruber]

> I tried to make this pr is dependent on #4968. Hope this works...
> 
> The change fixes a test issue in gc/g1/TestMixedGCLiveThreshold.java by adding
> the option `-XX:ParallelGCThreads=1`. This prevents the full gc from running
> with more than one worker because if it would do that, live data could be
> distributed into several regions and one of them could be selected for
> collection which is unexpected with `-XX:G1MixedGCLiveThresholdPercent=25`.
> 
> Please refer to the JBS-Item for more details.
> 
> Thanks, Richard.

Richard Reingruber 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 three additional commits since the last revision:

 - Merge branch 'master'
 - 8271722: [TESTBUG] gc/g1/TestMixedGCLiveThreshold.java can fail if G1 Full GC uses >1 workers
 - start

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4971/files
  - new: https://git.openjdk.java.net/jdk/pull/4971/files/7d759975..3762a0dc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4971&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4971&range=01-02

  Stats: 1876 lines in 109 files changed: 1339 ins; 342 del; 195 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4971.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4971/head:pull/4971

PR: https://git.openjdk.java.net/jdk/pull/4971