Add nosexunit as a pip requires.

Install the nose xunit plugin so that tempest can produce nice
reports in Jenkins.

Change-Id: Ia8c4c9db8b0733d09a0bef59a08f438c6a92f1ca
diff --git a/files/pips/tempest b/files/pips/tempest
index df7f423..6eeb5b9 100644
--- a/files/pips/tempest
+++ b/files/pips/tempest
@@ -1 +1,2 @@
 pika
+nosexunit  # For use by jenkins in producing reports