pip update virtualenv in tox-install

pip update virtualenv in tox-install

tox calls system virtualenv which breaks the coala linter.
as well as bringing with it a a very old version of pip from system.
updating virtualenv fixes this.

Also, envlist no longer has py35,py36,py37
so remove pins that were for supporting old python version

removed python2 workarounds.
-python3 -m nltk.downloader ect

Also removed
-passenv = TOX_WORK_DIR
-toxworkdir = {env:TOX_WORK_DIR:/tmp/v}

This was added in 11728
"By default tox environment will now be installed under /tmp/v/{envname}
but configurable through the CLI environment by specifying
TOX_WORK_DIR."

builder-jjb-merge and builder-jjb-verify to not call tox.
So it would not help with opnfv race conditions with multiple jjb
verify/deploys running on a static builder.
there are actually no tox jobs for opnfv/releng repo.

Pretty sure this does nothing and just adds a layer
of complexity that is not needed.
so removed.

ISSUE: RELENG-2366

Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>
Change-Id: I07875a62341e28860a81ee7b2149393c148be84b