Bug 1046815: Update mozharness configs

This almost re-syncs our mozharness config files with the "real" ones in mozharness. The remaining differences are a few references to /tools; I am trying to sort out those differences with Release Engineering, but that may take some time.
Hmm, so in best case this does nothing... and in worst case it confuses the next reader :)

Either way, we should ideally have pip install stuff before we commit the image. As jlal says immutability is desired. We can tag the docker image with a version number, allowing old revisions referencing an old docker image version to run, even if the mozharness and its dependencies have changed and we have made a new incompatible version of gecko-images.