Increase verbosity of test output

There's a known-to-fail test in another branch right now. If I didn't
know that and I was relying on Travis to catch the issue, I would not
be happy with the default level of output. (Specifically, the amount
of output in a list of file names is not enough IMHO. It it was a
different type of list, it might be okay)

tox.ini

@@ -33,7 +33,7 @@ commands=
 [testenv]
 deps = .[test]
 commands =
-   coverage run --rcfile={toxinidir}/.coveragerc --source=sbws -m pytest -s {toxinidir}/tests
+   coverage run -vv --rcfile={toxinidir}/.coveragerc --source=sbws -m pytest -s {toxinidir}/tests
 passenv =
   TRAVIS
   TRAVIS_JOB_ID