RFR(S) : 8183040 : update jdk/test/lib/Platform.java to use NIO file API

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8183040/webrev.00
> 
> 38 lines changed: 8 ins; 16 del; 14 mod; 

Hi all,

could you please review this small clean up of testlibrary classes which updates j.t.lib.Platform and j.t.l.SA.SATestUtils (as it now contains the methods which 8183040 was about) to use NIO file API?

testing: test/hotspot/jtreg/serviceability 
webrev: http://cr.openjdk.java.net/~iignatyev//8183040/webrev.00
JBS: https://bugs.openjdk.java.net/browse/JDK-8183040

Thanks,
-- Igor