RFR: 8011697(ScriptEngine "js" randomly means either "rhino" or "nashorn", but should instead select one)

Hi, Please review http://cr.openjdk.java.net/~sdama/8011697/webrev.00/ for https://bugs.openjdk.java.net/browse/JDK-8011697 Fix is to make sure ScriptEngineManager always returns a particular engine on all platforms consistently. Regards, Srinivas