Allow standard install of a custom Knative Serving (#851)
Allow standard install of a custom Knative Serving (#851)

* Allow standard install of a custom Knative Serving

Delegate the process in `start_latest_knative_serving()` to `start_knative_serving()` to the standard install can be used for custom testing as well.

* Quote $1

knative/test-infra,knative/test-infra,knative/test-infra