RFR: 8293819: sun/util/logging/PlatformLoggerTest.java failed with "RuntimeException: Retrieved backing PlatformLogger level null is not the expected CONFIG"

[Daniel Fuchs]

The sun/util/logging/PlatformLoggerTest.java is missing a couple of Reference::reachabilityFence calls to maintain loggers alive while the test is running. It has been observed failing under stress.

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Commit messages:
 - Update Copyright year
 - 8293819

Changes: https://git.openjdk.org/jdk/pull/10284/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10284&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293819
  Stats: 10 lines in 1 file changed: 5 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/10284.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10284/head:pull/10284

PR: https://git.openjdk.org/jdk/pull/10284