RFR: JDK-8228990: JFR: TestNetworkUtilizationEvent.java expects 2+ Network interfaces on Linux but finding 1

[Erik Gahlin]

Could I have a review of a PR that changes the test for the Network Utilization event so it only validates the loopback interface. 

The test fail intermittently on the real network interface, so it's been on the problem list for years. This means the event hasn't got any testing. If there is an interest and resources to investigate this further, a separate issue can be filed to add back testing for more than the loopback interface.

Testing: 
Running /test/jdk/jdk/jfr/event/runtime/TestNetworkUtilizationEvent.java 400 times on Mac, Linux and Windows.

Thanks
Erik

-------------

Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/8841/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8841&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8228990
  Stats: 16 lines in 2 files changed: 0 ins; 12 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8841.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8841/head:pull/8841

PR: https://git.openjdk.java.net/jdk/pull/8841