RFR: 8336257: Additional tests in jmxremote/startstop to match on PID not app name

[Kevin Walls]

Follow-on from JDK-8207908.

Two tests are broken by that change:
sun/management/jmxremote/startstop/JMXStartStopTest.java	
sun/management/jmxremote/startstop/JMXStatusPerfCountersTest.java

These are additional tests which use jcmd and an application name pattern to find a process.
They should use the PID to avoid finding a process from some other concurrent test invocation.
So it's good to have the same kind of change applied here too.

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Commit messages:
 - 8336257: Additional tests in jmxremote/startstop to match on PID not app name

Changes: https://git.openjdk.org/jdk/pull/20138/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20138&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336257
  Stats: 7 lines in 2 files changed: 3 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20138.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20138/head:pull/20138

PR: https://git.openjdk.org/jdk/pull/20138