recovery: Provide sideload cancellation

We can't use InterruptWaitKey() as it hangs recovery
when called from the minadbd listener thread, so provide
our own 'CancelWaitKey' implementation.
[forkbomb: rework for Q]

Squashed:
  recovery: Move sideload (non)cancellation to its own key

   * We use KEY_REFRESH for actually refreshing menus, which is
     useful when handling hotpluggable storage.
     We don't want that to interact with the sideload menu.

  Change-Id: Id7f5c06385e613648b3f727fc5e91eb3206406cf

Change-Id: I13f0c9ae5444652a2141442ef24258679a78d320