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
Merge branch 'feature/fix-apache-nginx-race' into develop