RFR: JDK-8215991: Stop hiding exception from ArtifactResolver failures in tests

[Tim Bell]

Erik:

> In the test lib, we have an ArtifactResolver which is used by tests that
> need external resources. Internally at Oracle we hook Jib into this to
> provide such dependencies. For other users, it's possible to specify the
> path to such a dependency using a system property.
>
> If something goes wrong while resolving the dependencies, the
> ArtifactResolver currently swallows the exception and falls back on the
> default property based resolver, making it hard to figure out the problem.
>
> If the user provided the environment for calling Jib, I don't think we
> should try to revert to the default resolver on exception, but instead
> the exception should be propagated to the test.
>
> Webrev: http://cr.openjdk.java.net/~erikj/8215991/webrev.01/
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215991

Looks good.

Tim