fix for langtools intermittent failures needs to check PRODUCT_HOME

This bug clones JDK-8167600. The fix for that check JT_JAVA for 32 bit data model, but it needs to check jdk pointed at by PRODUCT_HOME.
JT_JAVA is the java used to run jtreg not the java being tested.

Running langtools tests using makefiles (ie., jib make run-test) results in intermittent failures most of the time on windows-x86. Mach 5 did not see intermittent failures before switching to using make for testing.
Most failures are errors in the form of timeouts or Agent communication errors. Maybe some default settings can be adjusted to all the default run to pass with no failures.
Since langtools tests which are failing are tier1, this may be higher priority than P3.