RFR: 8342570: gc.*.gcUntilOld() assumes that full gc always promotes objects to old generation in a generational heap

[Y. Srinivas Ramakrishna]

This is a draft while we go over the issues in the ticket.

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Commit messages:
 - Remove debugging debris
 - Merge branch 'master' into test_cleanup
 - Changes identical to PR 527 for JDK-8342734.
 - Merge branch 'master' into test_cleanup
 - Merge branch 'master' into test_cleanup
 - Debugging cruft, not for checkin.
 - Tweak documentation comment, explicating that non-generational
 - Move the override of CollectedHeap::full_gc_promotes_to_old() from the
 - Merge branch 'master' into test_cleanup
 - JDK-8342570  gc.*.gcUntilOld() assumes that full gc always promotes objects to old generation in a generational heap

Changes: https://git.openjdk.org/shenandoah/pull/521/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=521&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342570
  Stats: 51 lines in 10 files changed: 39 ins; 8 del; 4 mod
  Patch: https://git.openjdk.org/shenandoah/pull/521.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/521/head:pull/521

PR: https://git.openjdk.org/shenandoah/pull/521