Review request 8072656: test/java/lang/reflect/Proxy/ClassRestrictions.java assumes app class loader be URLClassLoader

[Mandy Chung]

http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8072656/webrev.00/

This updates the test to get the classpath from "test.classes" system 
property and pass it to the custom class loader (instead of calling the 
getURLs() method of the app class loader).

Mandy