Pulp

pulp_celerybeat currently can only be run in one process per deployment, and it is one of the single points of failure in Pulp. Multiple instances of pulp_celerybeat should be able to run concurrently.

Deliverables:

1) Modify Pulp to be able to run multiple pulp_celerybeat process concurrently
2) Ensure that Pulp scheduled calls occur only once even with multiple pulp_celerybeat processes running
3) Ensure that even if pulp_celerybeat processes start being killed, that scheduled calls still dispatch only once.
4) Document changes
5) Add a release note
6) Verify that the failure watcher code is safe to run concurrently
7) Verify that the EventMonitor code is safe to run concurrently
8) Verify that the WorkerTimeoutMonitor code is safe to run concurrently