RFR: JDK-8164301: jib should provide a JDK to for running jtreg with

[Tim Bell]

Erik:

> When running tests via "jib make --profile run-test", jib does not set
> JT_JAVA (the JDK used to run the jtreg harness). This change makes Jib
> set the bootjdk as JT_JAVA. It also makes the same change in the top
> level makefiles when running "make test".
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8164301
>
> Webrev: http://cr.openjdk.java.net/~erikj/8164301/webrev.01/

Looks good.  Approved.

/Tim