kubernetes_e2e.py: remove working dir check if --build is specified

[saschagrunert]

The job pull-release-cluster-up is failing right now with:

+ /workspace/scenarios/kubernetes_e2e.py --build=quick --cluster= --down=false --extract=local --gcp-node-image=gci --gcp-nodes=4 --gcp-zone=us-west1-b --provider=gce --test_args=--ginkgo.focus=definitely-not-a-real-focus --timeout=65m
Traceback (most recent call last):
  File "/workspace/scenarios/kubernetes_e2e.py", line 391, in <module>
    main(parse_args())
  File "/workspace/scenarios/kubernetes_e2e.py", line 259, in main
    raise ValueError(k8s)
ValueError: /home/prow/go/src/github.com/kubernetes/release

Reason for that is that the current working directory is already /home/prow/go/src/github.com/kubernetes/release while the script expects to be in kubernetes/kubernetes. It does not seem to matter much for kubetest in which working directory we are, means we can remove the check completely. Also the method add_k8s does not do anything at all which means we can remove it, too.

cc @kubernetes/release-engineering

Should fix kubernetes/release#3588

[xmudrii]

/lgtm

[k8s-ci-robot]

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[aojea]

/assign @BenTheElder

did't we freeze this script?

[BenTheElder]

/hold

Please stop using scenario scripts. These are a holdover from bootstrap.py.

All jobs should be using prow decorate: true and kubetest2 or their own CI scripts

[BenTheElder]

These have been deprecated since 2018 and we've eliminated most of the users https://github.com/kubernetes/test-infra/tree/master/scenarios

[saschagrunert]

@BenTheElder I see. We have to move away from push-build.sh, then we can also remove those pull-release-cluster-up jobs. It's still used in kubetest1 and various other places. Do we have any plans to remove kubetest1 sooner than later?