Tox is called from system python2

which tox
/usr/bin/tox
tox --version
3.14.5 imported from
/usr/lib/python2.7/site-packages/tox/__init__.pyc

if $PYTHON=python3 we are not updaing tox
to the lastest version.

for some reason running this old tox
broke things. this appears to fix.

Also revert the lfenv stuff that we
don't want in tox-run

Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>
Change-Id: I2f964ec5123bd4a3b5fcc75f3d1ba38c0810cd8a