Completed framework update streams may retry forever

Since the agent/RP currently does not GC operation status update streams when frameworks are torn down, it's possible that active update streams associated with completed frameworks may remain and continue retrying forever. We should add a mechanism to complete these streams when the framework becomes completed.

A couple options which have come up during discussion:

• Have the master acknowledge updates associated with completed frameworks. Note that since completed frameworks are currently only tracked by the master in memory, a master failover could prevent this from working perfectly.
• Extend the RP API to allow the GC of particular update streams, and have the agent GC streams associated with a framework when it receives a ShutdownFrameworkMessage. This would also require the addition of a new method to the status update manager.