RFR: JDK-8313670: Simplify shared lib name handling code in some tests

[Matthias Baesken]

There is coding e.g. in
https://github.com/openjdk/jdk/blob/master/test/jdk/jdk/jfr/event/runtime/TestNativeLibrariesEvent.java#L72
that deals with shared lib naming on different OS.
This code should be simplified.

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Commit messages:
 - JDK-8313670

Changes: https://git.openjdk.org/jdk/pull/15151/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15151&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313670
  Stats: 77 lines in 6 files changed: 13 ins; 59 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/15151.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15151/head:pull/15151

PR: https://git.openjdk.org/jdk/pull/15151