[Release Pipeline] Use docker.io rather than gcr.io when running TE tests

[dkijania]

When running stable pipeline we are running integration tests as part of post release verifications. However, in release pipeline usually we are pushing to docker.io (this mechanism is based on tags which are not a part of pipeline but pre-manual step). Script which runs tests is always using gcr.io as a repository from which it fetches dockers. This can lead to lack of proper chain of build -> release -> test actions. We are releasing on docker.io but still we are testing images from gcr.io.

We need to introduce logic to run_test_executive script which should be aware that we want to pull from docker.io in some cases