Add Zookeeper to tests

Add a requirement on kazoo and add a Zookeeper chroot to the test
infrastructure.

This is based on similar code in Nodepool.

Change-Id: Ic05386aac284c5542721fa3dcb1cd1c8e52d4a1f
diff --git a/requirements.txt b/requirements.txt
index ec0b76a..4c5adc7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -16,3 +16,4 @@
 babel>=1.0
 six>=1.6.0
 ansible>=2.0.0.1
+kazoo