Couple Istio and Knative installation between test-infra and serving

[adrcunha]

knative/serving has its own serving installation function (https://github.com/knative/serving/blob/b5ae99b62303ff31437ba49b7fe48a664a74bdae/test/e2e-common.sh#L123), while all other repos use a standard function from knative/test-infra (

test-infra/scripts/library.sh

Line 302 in 0125a23

function start_latest_knative_serving() {

).

If these two functions are out-of-sync, updates to knative/serving might block E2E tests (presubmits and CI) in all the other repos (e.g., #674).

[adrcunha]

One simple (short-term?) solution would be adding an extra E2E test to serving that uses the function in library.sh to bring up serving.

[jessiezcc]

Pls sync up with @adrcunha on short term vs long term preference.

[adrcunha]

With Knative Serving 0.6 this is now obsolete, as installing it is now a single yaml. Closing as obsolete.