RFR 8202581: failure_handler: gather more environment information on macOS

[Amy Lu]

On macOS systems, the system configured proxy setting are used by the 
Java runtime by default. It will be helpful if system proxy 
configuration information can be collected in case of test failures.

Please review the enhancement to failure handler to help test failure 
analysis on macOS. Following environment information gathering added:

scutil --proxy

And together with:
scutil --nwi
ifconfig -a

bug: https://bugs.openjdk.java.net/browse/JDK-8202581
webrev: http://cr.openjdk.java.net/~amlu/8202581/webrev.00/

Thanks,
Amy