Added functionality to return list of rabbit hosts

In the process of adding this functionality, refactored the way search
occurs, so we can use a genericized method.
  * Added `#rabbit_servers` method, which returns a list of rabbit servers.
  * The `#memcached_servers` method no longer accepts an environment.
  * Re-factored methods which search to a generic `#search_for`.
  * Updated the tests which were modified to the new rspec expect syntax.

Change-Id: Ifb4dd793f47a6b7529c5fa9e65895d1bcab8f7b3
Merge "Added functionality to return list of rabbit hosts"