(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 don't know how many tests there will be in the future so it seems like a good idea to help future brogrammers out here.

But also the `#poll_jenkins_job` block also used to test for the exit status on job failure until you suggested that functionality for the method was overreaching. I moved the `exit 1` on build failure to the rake task and deleted the test but left potentially useful constructs in.

Read: I was too lazy to do anything more than remove the unnecessary testcase.