[8u] approval request for JDK-8141541: Simplify Nashorn's Context class loader handling

[Sundararajan Athijegannathan]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8141541

jdk9 review thread:
http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-November/005530.html

jdk8u webrev: http://cr.openjdk.java.net/~sundar/8141541/8u/webrev.00/

Backported "as is" without any changes except for modular source layout
difference.

Thanks,

-Sundar