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.
Yeah, I didn't see any protections, so we should make sure the resource_manager won't assign work to the wrong workers. It's possible there were already some protections in place, but you should double check to be sure.