QueryMaster must send the query finish heartbeat.

In the current implementation, QueryMaster only depends on its heartbeat thread for all kinds of reports. When a query master task without any succeeded report is moved to the finished list, the finish report may be omitted. As a result, QueryJobManager occasionally does not update the finish state (e.g., finish time and query state) for some queries even though the queries are already finished. This patch fixes this bug.