This currently installs with pip --user which cases problems if you
try to run this version of tox as another user. This is done in
system-config, for example, where we run tox with "become: yes" to run
testinfra.
By installing tox into a venv, we can call it as another user and it
just works because it's all encapsulated in the venv. We use the
virtualenv commands exported by ensure-pip to create this.
I think the original motivation for installing tox like this was to
ensure it is done without sudo permissions. This also doesn't require
permissions, but ensures the resulting tox_executable is able to be
executed in more contexts.
Needed-By: https://review.opendev.org/712819
Change-Id: Iebee8cb72cce7944c537fdb91b6c98ed51878661
6d78fc4f90