RFR: JDK-8232569: Use test image from different jib profile for testing

[Tim Bell]

Erik:

> Building and publishing a test image for every Jib build profile is a 
> waste of resources. We need to be able to specify a test image from a 
> different profile at test time when running "run-test-prebuilt". This 
> patch takes the concept used for the -jcov profiles and makes it more 
> general.
> 
> Webrev: http://cr.openjdk.java.net/~erikj/8232569/webrev.jdk14.01/
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8232569

Looks good.

Tim