Add unique_id to homematic_cloud (#16828)

* add unique_id

* add docstring and trigger travis

homeassistant/components/homematicip_cloud/device.py

@@ -61,6 +61,11 @@ class HomematicipGenericDevice(Entity):
         """Device available."""
         return not self._device.unreach
 
+    @property
+    def unique_id(self):
+        """Return a unique ID."""
+        return "{}_{}".format(self.__class__.__name__, self._device.id)
+
     @property
     def icon(self):
         """Return the icon."""