This patch is part of the community goals to enable python 3 first, and
only use python 2 when explict.
To do so, this patch:
- Makes python 3 the default env for non py27 tox targets.
- Addresses any py3 changes in the code.
Change-Id: Iab52979bb720a8df8924108093e5119922622cb9
ab3822413e