Review Request: 8006828: "SKIP_BOOT_CYCLE=false" must work in new building infrastructure

[Erik Joelsson]

Adding check for SKIP_BOOT_CYCLE=false in Jprt.gmk which adds the target 
bootcycle-images. Also fixing an issue with bootcycle-images target that 
prevented them from creating images.

http://cr.openjdk.java.net/~erikj/8006828/webrev.root.01/
/Erik