RFR: 8149599: Update Minefield test

[Jonathan Gibbons]

This is a change to re-enable the venerable MineField.sh test, which has 
been somewhat hacked and eventually disabled during the development of 
Project Jigsaw.

While cleaning up and translating the test into Java code, it uncovered 
a bug in classpath handling in the runtime (JDK-8156989, already fixed 
by Alan B), and so the shell form of the test has been given a stay of 
execution for a while.

There is a comment in the code to explain the rationale for the JDK 9 
cleanup.

JBS:  https://bugs.openjdk.java.net/browse/JDK-8149599
Webrev: http://cr.openjdk.java.net/~jjg/8149599/webrev.01/

webrev.00 has the test case that exposed JDK-8156989 commented out; 
webrev.01 has that test case enabled.

-- Jon