test: use tox isolated environments

Enable tox isolated environments to perform build operations in a virtual
environment.
See https://tox.wiki/en/latest/config.html#conf-isolated_build

Co-Authored-By: Ofek Lev <ofekmeister@gmail.com>
Signed-off-by: Joshua Lock <jlock@vmware.com>

Author: joshuagl

tox.ini

@@ -4,6 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
+isolated_build=true
 envlist = lint,docs,py
 skipsdist = true