Added keyword Clean Up All Nodes to kill stale lxc processes in Suite Teardown

Change-Id: Iac5367cb5eb6158a1897ff05ff2fa1f77a6e3111
diff --git a/tests/functional/Voltha_ErrorScenarios.robot b/tests/functional/Voltha_ErrorScenarios.robot
index a9e53d6..7f51af7 100755
--- a/tests/functional/Voltha_ErrorScenarios.robot
+++ b/tests/functional/Voltha_ErrorScenarios.robot
@@ -332,3 +332,4 @@
     #Restore all ONUs
 #    Run Keyword If    ${has_dataplane}    RestoreONUs    ${num_onus}
     Close All ONOS SSH Connections
+    Run Keyword If    ${has_dataplane}    Clean Up All Nodes