os/bluestore: reap ioc when stopping aio_thread.

there is possibillity that reap_ioc don't excute when stopping
aio_thread. so add reap_ioc after aio_thread is stopped.

Signed-off-by: Haodong Tang <haodong.tang@intel.com>

src/os/bluestore/KernelDevice.cc

@@ -237,6 +237,7 @@ void KernelDevice::_aio_stop()
     aio_stop = true;
     aio_thread.join();
     aio_stop = false;
+    reap_ioc();
     aio_queue.shutdown();
   }
 }