Don't use python 3

Don't use python 3

Now there are not files that require python 3, so for now just remove
the python 3 dependency and use python 2. I think the right plan is to
just get all of the python ready for python 3, and then use whatever
python is available.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
cc: 12.0 <mesa-stable@lists.freedesktop.org>