Document zuul client

Adds programoutput sphinx extension as a test dependency so doc
builds can include the program help text.

Change-Id: Iec2f09f710162614cbb393a5628204ddebe2e29f
diff --git a/test-requirements.txt b/test-requirements.txt
index 90d4934..9afa822 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -9,3 +9,4 @@
 python-subunit
 testrepository>=0.0.17
 testtools>=0.9.32
+sphinxcontrib-programoutput