RFR: JDK-8023765 -- Improve MaxPathLength.java testcase and reduce its test load

[Dan Xu]

Hi All,

MaxPathLength.javais a troublesome testcase, and fails intermittently in 
the nightly test. And it also runs for a long time, especially on 
Windows platforms. Inorder to improve the test stability, I remove its 
unnecessary test iterations, and use NIOdelete method todo the clean-up 
to make the potential failureseasier for diagnosis. Please review 
thechanges. Thanks!

bug: https://bugs.openjdk.java.net/browse/JDK-8023765
webrev: http://cr.openjdk.java.net/~dxu/8023765/webrev/

-Dan