RFR: JDK-8059658: Bootcycle build not actually using built image

[Tim Bell]

Hi Erik:

> Here is a fix for the bootcycle-images target. In JDK-8033119, the 
> definitions of the variables for JAVAC, JAR etc changed and 
> bootcycle-spec.gmk wasn't updated to match.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8059658
> Webrev: http://cr.openjdk.java.net/~erikj/8059658/webrev.root.01

Looks good to me.

Tim