erp5testnode: Add the protocol name to nat-rule-port

Now the nat-rule-port always has the protocol name, see here:
https://lab.nexedi.com/nexedi/slapos/blob/9a886c4b0c6dd229564292eaa0ef2604fa857aea/software/kvm/instance-kvm.cfg.jinja2#L843
Status Job ID Name Coverage
  External
passed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch-Boxiang

00:40:13

passed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch-Boxiang

00:36:08

passed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch-Boxiang

00:38:11

failed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch-Boxiang

15:03:01