RFR: JDK-8050922 - add additional diagnostic to java/net/MulticastSocket/TestInterfaces.java

[Mark Sheppard]

Hi,
    please oblige and review the following diagnostic output addition to
the test java/net/MulticastSocket/TestInterfaces.java

http://cr.openjdk.java.net/~msheppar/8050922/webrev/

for the task

https://bugs.openjdk.java.net/browse/JDK-8050922

which will assist in diagnosing an intermittent failing test
https://bugs.openjdk.java.net/browse/JDK-8041677

the addition displays the interface details, of the failing scenario,  
to std err

regards
Mark