test-network: add a line break after starting networkd

This may be ugly. But otherwise, outputs of several check commands
are shown without new line...

test/test-network/systemd-networkd-tests.py

@@ -141,6 +141,7 @@ class Utilities():
         else:
             subprocess.check_call('systemctl restart systemd-networkd', shell=True)
         time.sleep(5)
+        print()
 
 global ip
 global port