[host] windows: fix graceful exit

We were using an auto-reset event to signal the mousehook exit. This was
fine when there was only one thread, but with the addition of the update
thread, only one thread is signaled, causing the wait to last forever.

The fix is switching to a manual reset event and call ResetEvent after
the threads have exited.

host/src/app.c

@@ -787,6 +787,7 @@ fail_lgmp:
 fail_ivshmem:
   ivshmemClose(&shmDev);
   ivshmemFree(&shmDev);
+  DEBUG_INFO("Host application exited");
   return exitcode;
 }