Enable test/javax/script/GetInterfaceTest.java again

test/javax/script/GetInterfaceTest.java was disabled due to nashorn bug JDK-8010199: javax.script.Invocable implementation for nashorn does not return null when matching functions are missing

But 8010199 has been fixed. So GetInterfaceTest can be enabled again - with the following changes:

* Nashorn does not support implementing non-public interfaces. Interfaces in the test to be made public
* println->print replacement in script