RFR: JDK-8199352: The Jib artifact resolver in test lib needs to print better error messages

[Erik Joelsson]

The Jib artifact resolver is not very good at telling us why things go 
wrong. The reason is that it swallows exceptions. This patch changes the 
API from throwing a FileNotFoundException, which I don't really think 
fits correctly in all cases, to a new API specific exception.

I have greped for all uses of this API in the tests and changed the 
exception type caught at the caller location. I verified that I didn't 
break anything by compiling all the affected test classes and by running 
some of them for a bit.

With these changes it should be easier to diagnose problems with 
resolving artifacts in the future.

Bug: https://bugs.openjdk.java.net/browse/JDK-8199352

Webrev: http://cr.openjdk.java.net/~erikj/8199352/webrev.01/index.html

/Erik