RFR: JDK-8273246 Amend the test java/nio/channels/DatagramChannel/ManySourcesAndTargets.java to execute in othervm mode

[Mark Sheppard]

A number of nio DatagramChannel tests are intermittently failing on macosx-aarch64.
In some instances this is a receive call blocking indefinitely waiting on data which has
already been sent, and should be available immediately to the receive method call.
Other test failure scenarios are problems during the test compilation phase with a SocketException being thrown and the message:
"test result: Error. Agent communication error: java.net.SocketException: No buffer space available; check console log for any additional details"

The ManySourcesAndTargets and other tests execute in agentvm mode. This results in certain test diagnostic
Output being lost during the test failure handling capture process. To mitigate this lost diagnostics, the
ManySourcesAndTargets test has been amended to execute in othervm mode.

Additionally, to assist in the buffer allocation issue, the netstat command executed by the test
failure_handler has an extra argument added to obtain additional details on mbuf usage.
The failure handler will now execute with netstat -mm

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Commit messages:
 - JDK-8273246 Amend the test java/nio/channels/DatagramChannel/ManySourcesAndTargets.java to execute in othervm mode

Changes: https://git.openjdk.java.net/jdk/pull/5366/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5366&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273246
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5366.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5366/head:pull/5366

PR: https://git.openjdk.java.net/jdk/pull/5366