[jdk21u-dev] RFR: 8305931: jdk/jfr/jcmd/TestJcmdDumpPathToGCRoots.java failed with "Expected chains but found none"

[Robert Toyonaga]

This is a backport of https://github.com/openjdk/jdk/commit/65be5e0c547d74ca7de288b164aa9bd6d6855685

This change to JFR test code is needed because `TestJcmdDumpPathToGCRoots` transiently fails because it can't guarantee the expected objects are sampled.  The change improves cleanups between checks and also adds retries. 

This should help resolve some test failures for Adoptium (see https://github.com/adoptium/aqa-tests/issues/2766)

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Commit messages:
 - Backport 65be5e0c547d74ca7de288b164aa9bd6d6855685

Changes: https://git.openjdk.org/jdk21u-dev/pull/501/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=501&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305931
  Stats: 39 lines in 1 file changed: 7 ins; 0 del; 32 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/501.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/501/head:pull/501

PR: https://git.openjdk.org/jdk21u-dev/pull/501