RFR: 8297742: Combine vmTestbase/nsk/monitoring/ThreadMXBean/resetPeakThreadCount tests

[Alex Menkov]

The fix combines almost the same tests to 1 test to remove code duplication

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Commit messages:
 - Combined nsk resetPeakThreadCount tests

Changes: https://git.openjdk.org/jdk/pull/11400/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11400&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297742
  Stats: 289 lines in 7 files changed: 42 ins; 245 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11400.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11400/head:pull/11400

PR: https://git.openjdk.org/jdk/pull/11400