Fix the missing environment varible of CI.

Author: tonyseek

tox.ini

@@ -18,7 +18,9 @@ commands = flake8 {posargs}
 [testenv]
 usedevelop = True
 install_command = pip install {opts} {packages}
-setenv = VIRTUAL_ENV={envdir}
+setenv =
+    VIRTUAL_ENV={envdir}
+    ZOOKEEPER_VERSION={env:ZOOKEEPER_VERSION:}
 deps = -r{toxinidir}/requirements.txt
     -r{toxinidir}/requirements_sphinx.txt
 commands = {toxinidir}/ensure-zookeeper-env.sh nosetests {posargs: -d -v --with-coverage kazoo.tests}