RFR: 8268779: ZGC: runtime/InternalApi/ThreadCpuTimesDeadlock.java#id1 failed with "OutOfMemoryError: Java heap space"

[Per Liden]

Please review this fix for a ZGC shutdown/abort issue, introduced by JDK-8261759.

If a GC cycle has aborted, we should not notify that it completed and we should not check for out of memory condition. Doing so can cause pre-mature `OutOfMemoryError`.

Testing:
 - Tier 1-7 with ZGC on Linux/x86_64.
 - Wrote a small reproducer that provokes the problem fairly quickly. With this patch, I can no longer reproduced the issue.

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Commit messages:
 - 8268779: ZGC: runtime/InternalApi/ThreadCpuTimesDeadlock.java#id1 failed with "OutOfMemoryError: Java heap space"

Changes: https://git.openjdk.java.net/jdk/pull/6236/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6236&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268779
  Stats: 8 lines in 2 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6236.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6236/head:pull/6236

PR: https://git.openjdk.java.net/jdk/pull/6236