Install libvirt ubuntu package on Travis.
diff --git a/.travis.yml b/.travis.yml
index c27cc7c..97f0522 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,7 @@
   apt:
     packages:
       - graphviz
+      - libvirt
 
 matrix:
   fast_finish: true