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.
Same comments here as I wrote in the API docs - maybe we should take the opportunity to make these dicts instead of bools, just in case we want to add more data about them later without needing to wait for an X release?