views: set boot field to readonly

In edit client form, set boot field to read-only

Boot mode can be updated from Commands -> Set boot mode, it is more flexible to
do it from there, because you can select several clients and set the boot mode
at once.

ogcp/views.py

@@ -989,6 +989,7 @@ def action_client_update():
         available_modes.extend([(mode, mode) for mode in r.json()['modes']
                                 if mode != current_mode])
         form.boot.choices = list(available_modes)
+        form.boot.render_kw = {'readonly': True}
 
         r = server.get('/scopes')
         room_id = db_client['room']