Fix Apache and Nginx race condition with /var/www/html

Kibana uses `/var/www/html` as its web root and Nginx attempts to serve its static assets from there. Later, Apache is installed for the Graphite Web interface, and the Apache package dumps a test site into `/var/www/html`. Unfortunately, this overwrites the static assets that Kibana and Apache's test site have in common (`index.html`).

This changeset makes the Graphite installation go first, followed by Kibana. In addition, the Apache installation also removes the test site *if* `apache_delete_default_site` is `True`.

See also: https://github.com/azavea/ansible-apache2/pull/2