Make --run-test skip unnecessary testing on presubmit (#477)
Make --run-test skip unnecessary testing on presubmit (#477)

* Add --run-presubmit-tests flag to presubmit-tests.sh

presubmit-tests.sh is used by both presubmit and continuous jobs, they don't always execute the same set of tests. Add a flag to make it easier to separate. Also add logic to skip running tests for documentation only PRs if it's presubmit test

* remove the flag

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