RFR: 8317218: G1: Make TestG1HeapRegionSize use createTestJvm

[Leo Korinth]

Tested with:
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestG1HeapRegionSize.java JTREG='JAVA_OPTIONS=-XX:+UseG1GC'` -> PASS 1
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestG1HeapRegionSize.java JTREG='JAVA_OPTIONS=-XX:+UseZGC'` -> TOTAL 0
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestG1HeapRegionSize.java JTREG='JAVA_OPTIONS=-XX:G1HeapRegionSize=80000'` > TOTAL 0
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestG1HeapRegionSize.java JTREG='JAVA_OPTIONS='` -> PASS 1

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Commit messages:
 - 8317218: G1: Make TestG1HeapRegionSize use createTestJvm

Changes: https://git.openjdk.org/jdk/pull/15959/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15959&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317218
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15959.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15959/head:pull/15959

PR: https://git.openjdk.org/jdk/pull/15959