[jdk11u-dev] RFR: 8282642: vmTestbase/gc/gctests/LoadUnloadGC2/LoadUnloadGC2.java fails intermittently with exit code 1

[Goetz Lindenmaier]

I backport this for parity with 11.0.18-oracle.

I had to resolve and adapt the test description.
WhiteBox and ClassFileInstaller are at different locations in 11.

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Commit messages:
 - Backport 7db5abddd126db388b1a7f89be258e8aa7104da7

Changes: https://git.openjdk.org/jdk11u-dev/pull/1456/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1456&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8282642
  Stats: 18 lines in 1 file changed: 11 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1456.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1456/head:pull/1456

PR: https://git.openjdk.org/jdk11u-dev/pull/1456