Resource selection criteria can reference build parameters

You can now reference build parameters as variables in resource selection criteria:

![screen shot 2014-12-10 at 6 40 34 pm](https://cloud.githubusercontent.com/assets/163239/5388234/1cfd18ac-809c-11e4-99ab-9b862c64f3ac.png)

I apologize if there was a better way to implement this, this is my first time submitting a patch to Jenkins. Let me know if there is a better approach and I'll gladly update my PR.

Thanks!