Merge pull request #1881 from edx/feanil/add_graphviz_back

Add graphviz back since it is used by the CS188x class.

playbooks/roles/edxapp_common/defaults/main.yml

@@ -7,6 +7,8 @@ edxapp_common_role_name: edxapp_common
 edxapp_common_debian_pkgs:
     - build-essential
     - gfortran
+    # Needed for sandboxes for CS188x classes :-(
+    - graphviz
     - graphviz-dev
     - liblapack-dev
     - libmysqlclient-dev