Get artifacts from jobs higher in the upstream chain

Heya,

I need the plugin to be able to load artifacts from any upstream build that caused a build to be triggered. Not just the direct parent. So i added a recursive call to getBuild to make that happen.

Including unit test scenario with a grandparent job which has the artifact that the job wants.

Functionally tested in our environment with a job chain of four jobs where the artifact was at the top job.

If this is an interesting addition to the plugin please pull it in :-)

Cheers,

Hugo