Server refactorings

## Refactor zookeeper init setup for cloudera packages

Future runit support work make calls to `/etc/init.d/zookeeper` less than consistent, so instead we can invoke `/usr/bin/zookeeper-server-initialize` directly, as the zookeeper user.

Also, only the last package will be used to trigger the initialize command as it only needs to be run once.

## De-duplicate the service[zookeeper] resources in the server recipe.

We should be able to combine the `:enable` and `:start` actions into the single resource at the end of the server recipe.

## Add integration tests for CentOS & Cloudera packages.

This PR refactors the ServerSpec tests in the server suite to a common example group which can be shared among the other server suites. Pretty decent, no?