Raise N2VCNotFound exception in delete_namespace

Change-Id: I57d8ab115b4efdee65af2ca1e951463359ef81de
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/n2vc_juju_conn.py b/n2vc/n2vc_juju_conn.py
index 6b8ac09..bac0f2c 100644
--- a/n2vc/n2vc_juju_conn.py
+++ b/n2vc/n2vc_juju_conn.py
@@ -556,6 +556,8 @@
                     model_name=ns_id,
                     total_timeout=total_timeout
                 )
+            except N2VCNotFound:
+                raise
             except Exception as e:
                 raise N2VCException(message='Error deleting namespace {} : {}'.format(namespace, e))
         else: