8183503: Update hotspot tests to allow for unique test classes directory

[Alan Bateman]

jtreg has been updated via CODETOOLS-7902003 [1] to use a unique 
test.classes directory. This is part of improving the reliability when 
running tests concurrently. The change exposes issues in a small number 
of tests in the hotspot, jdk, and langtools repos and these issues will 
need to be fixed before the requiredVersion can be bumped to use a 
promoted jtreg with this change.

For the hotspot repo the tests in runtime/ClassUnload all fail with this 
change due to a class loader that the tests create and unreference to 
exercise class unloading. Easily fixed by changing the class loader to 
one that attempts to loads the class before delegation to the parent 
(this ensure the class is not loaded by the parent).  Another test that 
needed update is runtime/logging/ClassLoadUnlaodTest.java as it's a 
driver test and needs to start the child VM with test.class.path rather 
than test.classes. Finally one of the compiler tests wasn't locate the 
class bytes correctly so it needed an update too.

The webrev with the changes is here:
    http://cr.openjdk.java.net/~alanb/8183503/webrev/index.html

I'd like to push these to jdk10/jdk10 so that they can meet up with 
changes coming for related issues in the jdk and langtools repos.

-Alan

[1] https://bugs.openjdk.java.net/browse/CODETOOLS-7902003