RFR: 8305567: serviceability/tmtools/jstat/GcTest01.java failed utils.JstatGcResults.assertConsistency

[Kevin Walls]

There is no guarantee of consistency when sampling jstat data, and we're asserting these figures are always consistent.
Tests should retry some small number of times, rerunning the jstat tool to recapture data.

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Commit messages:
 - (C)
 - Common base class for Jstat tests
 - GCPerfTests retry

Changes: https://git.openjdk.org/jdk/pull/26094/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26094&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305567
  Stats: 98 lines in 9 files changed: 60 ins; 12 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/26094.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26094/head:pull/26094

PR: https://git.openjdk.org/jdk/pull/26094