RFR: 8321401: GenShen: Each mutator must see FullGC before throwing OOM

[Kelvin Nilsen]

Require each thread to observe unproductive Full GC before it throws OOM exception.

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Commit messages:
 - Fix test and remove conditionally compiled redundant code
 - Require full gc before throwing out-of-memory

Changes: https://git.openjdk.org/shenandoah/pull/365/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=365&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321401
  Stats: 15 lines in 2 files changed: 2 ins; 12 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/365.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/365/head:pull/365

PR: https://git.openjdk.org/shenandoah/pull/365