[8u60] Request for Approval: 8081668: fix Nashorn ant externals command

[Attila Szegedi]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8081668
jdk9 webrev: http://cr.openjdk.java.net/~mhaupt/8081668/webrev.00 <http://cr.openjdk.java.net/~mhaupt/8081668/webrev.00>
jdk9 review thread: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-June/004651.html <http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-June/004651.html>

Changes apply cleanly to jdk8u-dev after path reshuffling from modular source code layout.

Thanks,
  Attila.