(QENG-1225) Implement uber_build polling and status query.

I realize this still needs some work but wanted to get some eyes on it before doing much more with it. Some questions:
1. Is it okay to do what I've done with the Pkg::Util::Date.timestamp method? This ensures that we get the same `build_date` that was used to generate the dynamic jenkins job, thereby allowing subsequent rake invocations involving the new utility tasks to successfully query the build jobs. I figure this is okay because documentation for this repository recommends using package:implode before running again--is that accurate? Maybe I should re-read the documentation before making this assumption...
2. Which parts of this need spec tests? Are there spec tests for rake tasks? I could probably figure this out with enough digging around but I don't want to do more work than is necessary ;)
3. Are y'all okay with using net/http rather than curl commands? I know @haus mentioned he would have gone with curl commands...
I think it's cleaner to have this method return false or raise an exception if the job has failed and let the task handle that. Exiting here seems like an overreach for the method.