RFR(XS) : 8188117 : jdk/test/lib/FileInstaller doesn't work for directories

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8188117/webrev.00/index.html
> 5 lines changed: 2 ins; 0 del; 3 mod;

Hi all,

could you please review this tiny fix for testlibrary class?

FileInstaller uses Path::relativize incorrectly, it calls this method on a child passing (grand*)parent as an argument, but Path::relativize constructs a relative path for an argument against an receiver.
the patch also adds diagnostic output to help w/ failure analyses.

webrev: http://cr.openjdk.java.net/~iignatyev//8188117/webrev.00/index.html
JBS: https://bugs.openjdk.java.net/browse/JDK-8188117

Thanks,
-- Igor