RFR(XS): 8056930: Output host info under some condition for core dump

[Yumin Qi]

Please review

Bug:  https://bugs.openjdk.java.net/browse/JDK-8056930
Webrev:  http://cr.openjdk.java.net/~minqi/8056930/webrev00

   After java crashed, we would like to know the host on which it failed 
especially when doing parallel testing on multiple machines. The most 
useful for knowing host name is telling if the test is hardware related, 
that the test can only repeat on it.   This piece of code help to print 
out host name in debug mode.

   Test: manually tested on Unix/Linux/Windows with 
-XX:+CrashGCForDumpingJavaThread.
    JPRT

Thanks
Yumin