RFR: Restrict region dump to young

[Kelvin Nilsen]

We are primarily interested in the young-gen aged regions.  It is confusing for the log report to add the live data pertaining to old-gen regions which happen to have age > 0.

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Commit messages:
 - Merge remote-tracking branch 'GitFarmBranch/restrict-region-dump-to-young' into restrict-region-dump-to-young
 - Only report young regions in age-censue report at end of GC cycle

Changes: https://git.openjdk.org/shenandoah/pull/230/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=230&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/230.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/230/head:pull/230

PR: https://git.openjdk.org/shenandoah/pull/230