[FIX] hw_blackbox_be, hw_scale: don't rely on serial ID to be unique

After plugging in multiple identical serial to USB interfaces, only the
last one will be available under /dev/serial/by-id/ because they'll have
identical IDs. Instead use /dev/serial/by-path/ which does not have this
issue.

addons/hw_blackbox_be/controllers/main.py

@@ -37,7 +37,7 @@ class Blackbox(Thread):
     # request. The first device to give an answer that makes sense
     # wins.
     def _find_device_path_by_probing(self):
-        path = "/dev/serial/by-id/"
+        path = "/dev/serial/by-path/"
         probe_message = self._wrap_low_level_message_around("S000")
 
         try:

addons/hw_scale/controllers/main.py

@@ -29,7 +29,7 @@ class Scale(Thread):
         self.lock = Lock()
         self.scalelock = Lock()
         self.status = {'status':'connecting', 'messages':[]}
-        self.input_dir = '/dev/serial/by-id/'
+        self.input_dir = '/dev/serial/by-path/'
         self.weight = 0
         self.weight_info = 'ok'
         self.device = None