Use --tenant-id, not --tenant_id

Change-Id: I0e3d65d5b69ac82cbf7ee6ffc41ead369af8c126
diff --git a/lib/marconi b/lib/marconi
index 742f866..6b9ffdc 100644
--- a/lib/marconi
+++ b/lib/marconi
@@ -142,7 +142,7 @@
 
     MARCONI_USER=$(get_id keystone user-create --name=marconi \
                                                 --pass="$SERVICE_PASSWORD" \
-                                                --tenant_id $SERVICE_TENANT \
+                                                --tenant-id $SERVICE_TENANT \
                                                 --email=marconi@example.com)
     keystone user-role-add --tenant-id $SERVICE_TENANT \
                             --user-id $MARCONI_USER \