RFR: 8254102: use ProcessHandle::pid instead of ManagementFactory::getRuntimeMXBean to get pid in tests

[Igor Ignatyev]

Hi all,

could you please review this small cleanup which replaces
`ManagementFactory.getRuntimeMXBean().getName().split("@")[0]` w/ `ProcessHandle.current().pid()` to get current
process pid?

Thanks,
-- Igor

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Commit messages:
 - update copyright
 - use ProcessHandle::pid instead of ManagementFactory::getRuntimeMXBean to get pid

Changes: https://git.openjdk.java.net/jdk/pull/534/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=534&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254102
  Stats: 55 lines in 8 files changed: 0 ins; 41 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/534.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/534/head:pull/534

PR: https://git.openjdk.java.net/jdk/pull/534