Tweak test for differing unit name from iptables-persistent

We are starting to use iptables-persistent rather than custom scripting added to the iptables package that we were using in earlier versions of Apertis to apply iptables rules at boot. This package uses a systemd unit with a different name. Tweak the test to use the new name.

Signed-off-by: Martyn Welch martyn.welch@collabora.com