Review request for JDK-8138906

[Srinivas Dama]

Hello All,

Please review :
Bug : https://bugs.openjdk.java.net/browse/JDK-8138906
Webrev : http://cr.openjdk.java.net/~sdama/8138906/webrev.01

Fix is to pick 'java' from specified JAVA_HOME folder, along with this,
I have added some utility functions(can be added more) which can be used in all nashorn test case to make them work
Independent of underlying shell.(removed dependency on shell commands like : which)

Regards,
Srinivas