make the testr.conf required environment pass throught in tox

TrivialFix

Change-Id: I427bd3207de4ae87ab98dc024c4e2d98f0b572dd

tox.ini

@@ -10,6 +10,8 @@ install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
+          OS_STDOUT_CAPTURE OS_STDERR_CAPTURE OS_LOG_CAPTURE OS_TEST_TIMEOUT
+          PYTHON OS_TEST_PATH LISTOPT IDOPTION
 commands =
   find . -type f -name "*.pyc" -delete
   python setup.py test --slowest --testr-args='{posargs}'