RFR: 8315988: ParallelGC: Make TestAggressiveHeap use createTestJvm

[Leo Korinth]

Make TestAggressiveHeap use createTestJvm (so that the test forwards VM/JAVA_OPTIONS). The TestAggressiveHeap flag implicitly turns on the parallel gc, thus  `@requires vm.gc.Parallel`. 

Tested with:
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestAggressiveHeap.java JTREG="JAVA_OPTIONS=-XX:+UseParallelGC"` (PASS 1)
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestAggressiveHeap.java JTREG="JAVA_OPTIONS=-XX:+UseSerialGC"` (PASS 0)
`make run-test TEST=open/test/hotspot/jtreg/gc/arguments/TestAggressiveHeap.java`(PASS 1)

Started hs_tier1, hs_tier2 to see that we do not propagate conflicting flags.

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Commit messages:
 - 8315988: ParallelGC: Make TestAggressiveHeap use createTestJvm

Changes: https://git.openjdk.org/jdk/pull/15657/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15657&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315988
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15657.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15657/head:pull/15657

PR: https://git.openjdk.org/jdk/pull/15657