RFR(s): 8201518 add test for randomized iteration order of unmodifiable Set and Map

[Stuart Marks]

Hi all,

Please review this new test for testing the randomized iteration order of 
unmodifiable Set and Map implementations.

Bug:

     https://bugs.openjdk.java.net/browse/JDK-8201518

Webrev:

     http://cr.openjdk.java.net/~smarks/reviews/8201518/webrev.0/

Thanks,

s'marks