Corrected OOO with sensu needing rabbit

We have meta configs in some roles to run common, rabbit, and
sensu-client.  However, common and sensu-client are already
applied to every node.  Having the extra dependencies in each
role are a bit confusing.  Maybe it is better to add dependencies
inside the role, however, it looks clearer in the main site.yml.
Also, made sure rabbit is installed first.