osm.py: minor fix when using ns-list --long

Change-Id: I159c6644363e9cf071eae6353207a41fa9586197
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osmclient/scripts/osm.py b/osmclient/scripts/osm.py
index 6245bb3..d405d6d 100755
--- a/osmclient/scripts/osm.py
+++ b/osmclient/scripts/osm.py
@@ -230,7 +230,7 @@
         summary = ""
         n_nets = 0
         status_nets = {}
-        net_list = status_dict['nets']
+        net_list = status_dict.get('nets',[])
         for net in net_list:
             n_nets += 1
             if net['status'] not in status_nets: