Thanks to lifeless, pip now implicitly has a wheel cache so that it
builds a wheel before every install, and uses that cache. All our
clever attempts at manually doing wheelhouse things is actually
bypassing the existing cache and making things take longer.
We should remove all of this code and just let pip do this thing,
which is does very well, and get out of the way.
Change-Id: Ia140dc34638d893b92f66d1ba20efd9522c5923b
9013bb0c24