improve tox.ini with OS conventions

tox.ini

@@ -6,11 +6,13 @@ skipsdist = True
 [testenv]
 usedevelop = True
 install_command = pip install -U {opts} {packages}
-setenv =
-   VIRTUAL_ENV={envdir}
+setenv = VIRTUAL_ENV={envdir}
+         PYTHONDONTWRITEBYTECODE = 1
+         LANGUAGE=en_US
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands =
+    bash -c "TESTS_DIR=./redfish/tests python setup.py testr --slowest --testr-args='{posargs}'"
 
 [testenv:pep8]
 commands = flake8
@@ -33,4 +35,4 @@ commands = oslo_debug_helper {posargs}
 show-source = True
 ignore = E123,E125
 builtins = _
-exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build
+exclude = .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build