RFR: JDK-8218177: Bump jib format_version to support new devkit archive layout

[Erik Joelsson]

With the new devkits I deployed recently (Oracle internal), the file 
layout changed as a top level directory inside the tar archive was 
introduced. This works in most cases, but there are certain situations 
where jib does not handle this well. This causes AOT testing on Linux to 
stop working with the run-test-prebuilt make target.

This issue is being fixed in Jib, but to activate the fix a bump in the 
format_version is required. This patch does that, as well as adjusting 
to conform to the new behavior.

Bug: https://bugs.openjdk.java.net/browse/JDK-8218177

Webrev: http://cr.openjdk.java.net/~erikj/8218177/webrev.01/

(note that the Jib fix is not yet live in production)

/Erik