Add (and use) a new function find_hunt_for_hunt_id

Add (and use) a new function find_hunt_for_hunt_id

The code to call get_table_item with a hunt_id was broken, (since in
the schema, hunt_id is not the key, only channel_id is), so instead we
need to scan the table looking for a matching hunt_id. We already had
code to do this is find_hunt_for_channel, so here we factor that out
into a new function, find_hunt_for_hunt_id and call it instead of
get_table_item.