Move python version to python3

Remove pin workarounds for python2
install tox via python3 pip
so that the version of tox is run from
/home/jenkins/.local/lib/python3.6/site-packages/tox/__init__.py
fix release-job to use venv

Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>
Change-Id: I4b2d778f3fd81565c5dd009d50c969696faba0d2
Signed-off-by: Tim Johnson <tijohnson@linuxfoundation.org>