RFR 8055899: Two nashorn tests fail in 8u40 nightly build with ClassNotFoundException

[A. Sundararajan]

Please review http://cr.openjdk.java.net/~sundar/8055899/

Although I can't reproduce the ClassNotFoundException in my environment, 
I can see why it could fail where javafx is missing. or jfxrt.jar does 
not contain netscape.javascript.JSObject class. Modified tests to 
vacuously pass in case this class is missing.

Thanks,
-Sundar