* Update docs to use kubectl long flags
* adding back in the --filename flag (lost when manually merged)
* notice a few missed
* notice a few missed '-f' flags
* change -o to --output
* Update samples to not use Ingress.
This is follow-up of https://github.com/knative/serving/pull/1228. We
moved to Istio v1alpha3 / Gateway which requires a different way to
get the external IP address to send traffic to our samples.
* Also update the command to find service domain.