- Fix: call self.master.data.updates.buildslaveDisconnected when the Slave is disconnected
   This patch fix the following bug:
    - When a slave disconnects, the list "connected_to" in JSON object returns by http://127.0.0.1:8020/api/v2/buildslave
      isn't updated
 - Add buildslaveConfigured methods and update the db.
   It fix the following bug: "configured_on" was always an empty list
   when we made this HTTP Request http://127.0.0.1:8020/api/v2/buildslave
 - Update unittest