Adds test case for issue 301 (#447)
Adds test case for issue 301 (#447)

* Adds test case for issue 301

This adds a test case for issue # 301 and some related nested env-var item combinations.

* marked issue 301 test case as xfail()

tox-dev/tox,Avira/tox,loechel/tox,gaborbernat/tox,selimb/tox