[JDK 11] RFR 8202763: failure_handler: list open files for macOS

[Amy Lu]

In case of test failures, open files information are collected on Linux 
(lsof) and Windows (openfiles) but not macOS.

Please review the patch to add this information to macOS too, to help 
failure analysis.

bug: https://bugs.openjdk.java.net/browse/JDK-8202763
webrev: http://cr.openjdk.java.net/~amlu/8202763/webrev.00/

Thanks,
Amy