RFR: 8342734: GenShen: Test failure gc/shenandoah/TestReferenceRefersToShenandoah.java#generational

[William Kemper]

Recent change introduced a regression: https://bugs.openjdk.org/browse/JDK-8342560 that caused old regions to not belong to global collections.

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Commit messages:
 - Allow active global collections to contain old regions

Changes: https://git.openjdk.org/shenandoah/pull/527/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=527&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342734
  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah/pull/527.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/527/head:pull/527

PR: https://git.openjdk.org/shenandoah/pull/527