make new-net task wim parameter backward compatible

Change-Id: I90e0b0affa4c5350b9ace0000441e7ba022ea7f2
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>
diff --git a/osm_ro/vim_thread.py b/osm_ro/vim_thread.py
index 57ced9c..8d44f47 100644
--- a/osm_ro/vim_thread.py
+++ b/osm_ro/vim_thread.py
@@ -1003,7 +1003,9 @@
 
             net_name = params[0]
             net_type = params[1]
-            wim_account_name = params[3]
+            wim_account_name = None
+            if len(params) >= 4:
+                wim_account_name = params[3]
 
             sdn_controller = self.vim.config.get('sdn-controller')
             if sdn_controller and (net_type == "data" or net_type == "ptp"):