L2SS-183: Do not silently return but rethrow the DevFailed exception with an explanation

devices/devices/observation_control.py

@@ -284,8 +284,9 @@ class ObservationControl(Device):
             # Create the Observation device and instantiate it.
             self.create_dynamic_device(class_name, device_name)
         except DevFailed as ex:
-            self.error_stream("Cannot create the Observation device instance {} for ID={}.  This means that the observation did not start.".format(device_name, id))
-            return
+            error_string = "Cannot create the Observation device instance {} for ID={}.  This means that the observation did not start.".format(device_name, id)
+            self.error_stream(error_string)
+            Except.re_throw_exception(ex, "DevFailed", error_string, __name__)
 
         try:
             # Instantiate a dynamic Tango Device "Observation".