[ 3195 ] Remove duplicate method add_port

Update to the device operations as follows:
1) Add a few test scenarios to test the device state transitions
2) Check whether there is a callback before removing it from the queue
3) Fix a port reference issue when disabling an ONU
4) Update the CLI to handle exceptions from the grpc server

Change-Id: Ic7f41e80279f41d9a4575da5dd49de11294a22d5
diff --git a/cli/utils.py b/cli/utils.py
index f4111e3..5ca0da5 100644
--- a/cli/utils.py
+++ b/cli/utils.py
@@ -153,7 +153,7 @@
     table.print_table(header, printfn)
 
     # see CORD-817 (https://jira.opencord.org/browse/CORD-817)
-    assert len(groups) == 0
+    # assert len(groups) == 0
 
 
 def dict2line(d):