RFR: 8319161: GC: Make TestParallelGCThreads use createTestJavaProcessBuilder

[Leo Korinth]

`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS='` -> pass 1
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:ParallelGCThreads=42' ` --> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UseG1GC' ` --> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UseParallelGC' ` -> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UseSerialGC' ` -> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UseZGC' `-> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UseShenandoahGC' `-> total 0
`make run-test TEST=jtreg:test/hotspot/jtreg/gc/arguments/TestParallelGCThreads.java JTREG='VERBOSE=all;JAVA_OPTIONS=-XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC' ` -> total 0 

I will later (before integrating) run this test together with more tests through high tier testing to see that we do not fail when rotating flags.

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Commit messages:
 - 8319161: GC: Make TestParallelGCThreads use createTestJavaProcessBuilder

Changes: https://git.openjdk.org/jdk/pull/16434/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16434&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319161
  Stats: 9 lines in 1 file changed: 4 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/16434.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16434/head:pull/16434

PR: https://git.openjdk.org/jdk/pull/16434