In addition to Watch()es, we poll. The interval is currently hardcoded to 30m. Make it tunable, like SyncSetReapplyInterval.

NOTE TO CONSUMERS: This poll was introduced for HIVE-1510 and HIVE-1511 as a means to get remote MachineSet status changes back to the hub MachinePool. If you don't care about that, feel free to switch the poll off (set to zero). Otherwise, you are balancing responsiveness with performance.