Management events will now be dispatched via Zookeeper. The event queues
are namespaced by tenant since the event processing will later require a
tenant lock in a multi scheduler deployment.

Events are considered immutable once in the queue which eliminates the
need for a separate read/write lock. Because of this tenant
reconfiguration events are merged on-the-fly when consuming from the
queue instead of merging them on insert.

Change-Id: Ia79089ce87ab9f4921c38b4542bbf2ea3e655055