tests: Fix API change in sourceroute.py

Fix signature change introduced in http://gerrit.ovirt.org/#/c/34067

Change-Id: I4ba3b2a140f4bba82e40f8268dd40a6d90acc7bf
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35478
Reviewed-by: Dan Kenigsberg <danken@redhat.com>