RFR 8172493: Nashorn FX example 3-4 using load for fx: scripts fails to run with latest jdk9 ea build

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8172493/webrev.00/ for 
https://bugs.openjdk.java.net/browse/JDK-8172493

PS. I've not added an automated test because of javafx dependency [and 
the tests need to be run on openjdk builds as well]. I manually tested 
the fix using --patch-module option to replace build's nashorn classes 
with those of nashorn repo with the fix. The test shows the javafx 
window with a button as expected.

Thanks,
-Sundar