Update to new mqtt library

mqtt

@@ -1 +1 @@
-Subproject commit cf97fa066cdff0e2f7eda0ff4d3c8c0f59c3f2ec
+Subproject commit 14e56ccdbf6594f699b4afcfb4acafe9b899e914

piface_function.py

@@ -123,8 +123,11 @@ class pi_face(object):
         self._task_10ms.join()
 
     def stop(self):
-        self._task_10ms.stop()
-        self._task_10ms.join()
+        try:
+            self._task_10ms.stop()
+            self._task_10ms.join()
+        except AttributeError:
+            pass    # seems that there was an exception before init of task
         for i in range(0, 8):
             self.set_output(i, False)
         pifacedigitalio.deinit()