Manually trigger periodic task using controller api.

I discussed this with @mcvsubbu a bit. Setup controller api to allow for manually triggering a periodic task. When the controller gets a request to manually execute a periodic task, it will send a broadcast helix message to all the controllers in the cluster for executing the periodic task against the tables. Upon getting the broadcast message, each controller will run the specified periodic task against the tables for which it is the lead controller. Lead controllers will then respond back to the originating controller with status information regarding periodic task execution which will be returned back to the user for information purposes. It will also be useful to allow for fetching status information of recent periodic tasks executions (without necessarily manually executing a periodic task), so that user can find out status of recent periodic task executions.