Review Request: 8005635: build-infra: Support building install in jprt

[Erik Joelsson]

This is the open part of this review. The changes are mostly concerning 
compare logic and introducing a couple of new variables in spec for 
images directories.

Contributed by Tim Bell and myself.
http://cr.openjdk.java.net/~erikj/8005635/webrev.root.01/
http://cr.openjdk.java.net/~erikj/8005635/webrev.jdk.01/

/Erik