Updates to /status API

This patch returns additional data from the /status API call. Specifically, it
returns a worker list, the message broker connection status, the database
connection status, and the Pulp version (RHBZ #704184).

There is a small behavior change to include the resource manager and scheduler
as part of the worker heartbeat list. Previously, these were not included in
the list.
Do we need to use the factory for this? One of my long-term Pulp goals is to get rid of this module. I've found that a lot of our code can just be imported without involving this module, but not everything.