RFR: 8317317: G1: Make TestG1RemSetFlags use createTestJvm

[Leo Korinth]

Minor testing done, I will test more later with other fixes.

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Commit messages:
 - 8317317: G1: Make TestG1RemSetFlags use createTestJvm

Changes: https://git.openjdk.org/jdk/pull/15989/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15989&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317317
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15989.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15989/head:pull/15989

PR: https://git.openjdk.org/jdk/pull/15989