RFR: 8168369, , fix for langtools intermittent failures needs to check PRODUCT_HOME

[Tim Bell]

Hello

In the matter of intermittent test failures when run on 32-bit JVM 
installs.  My previous makefile fix [1] needs to check TESTJAVA instead 
of JT_JAVA.  Note: PRODUCT_HOME becomes TESTJAVA inside 
langtools/test/Makefile.

The bug report:
https://bugs.openjdk.java.net/browse/JDK-8168369

The webrev:
http://cr.openjdk.java.net/~tbell/8168369/

Thanks in advance-

Tim
[1] https://bugs.openjdk.java.net/browse/JDK-8167600