RFR: 8317228: GC: Make TestXXXHeapSizeFlags use createTestJvm [v3]

[Leo Korinth]

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

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  fix improvments requested by Stefan

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15986/files
  - new: https://git.openjdk.org/jdk/pull/15986/files/e0dde6f1..f0aaa67f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15986&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15986&range=01-02

  Stats: 3 lines in 2 files changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15986.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15986/head:pull/15986

PR: https://git.openjdk.org/jdk/pull/15986