Update tox to correctly use OS_TEST_PATH

Currently, to run unit tests, Patrole relies on a whitelist file
to separate unit tests from API tests so that tox -e py27/35 works.
However, this approach is hackish and has been abandoned in
favor of the following standard approach:

  - Use OS_TEST_PATH to .testr.conf
  - Override OS_TEST_PATH for unit test jobs in tox.ini
  - Remove the whitelist file as it's no longer needed

Change-Id: Iedbd01b539d24dc57e3c8bc1bb0dbb3ea9127ef4
diff --git a/tox.ini b/tox.ini
index d2e83e9..41e893c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,6 +8,9 @@
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
+   OS_TEST_PATH=./patrole_tempest_plugin/tests/unit
+   LANGUAGE=en_US
+   LC_ALL=en_US.utf-8
    PYTHONWARNINGS=default::DeprecationWarning
 passenv = OS_STDOUT_CAPTURE OS_STDERR_CAPTURE OS_TEST_TIMEOUT OS_TEST_LOCK_PATH OS_TEST_PATH http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 whitelist_externals = find
@@ -15,7 +18,7 @@
        -r{toxinidir}/test-requirements.txt
 commands =
     find . -type f -name "*.pyc" -delete
-    ostestr {posargs} --whitelist-file test-whitelist.txt
+    ostestr {posargs}
 
 [testenv:pep8]
 commands = flake8 {posargs}