RFR: 8303924: ProblemList serviceability/sa/UniqueVtableTest.java on Linux

[Alex Menkov]

The test fails intermittently on linux-x64-debug and linux-aarch64-debug

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Commit messages:
 - problemlist UniqueVtableTest on linux

Changes: https://git.openjdk.org/jdk/pull/12962/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12962&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303924
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12962.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12962/head:pull/12962

PR: https://git.openjdk.org/jdk/pull/12962