Use the dl.k8s.io CDN w/o slash for artifacts in kubetest2-ec2 jobs

[nrb]

Similar to a5a212f, which fixed a trailing slash for the cloud-provider-aws and sig-node jobs, this change ensures the kubetest2-ec2 jobs all use dl.k8s.io for their artifacts, rather than the gcsweb URL.

The --stage and --test-package-url parameters are also updated to not have a trailing slash, which results in 404s, such as in this job:
https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/kubernetes-sigs_provider-aws-test-infra/530/pull-kubernetes-e2e-ec2-cloud-provider-dual-stack-quick/2031854708028608512

That job used this command:

curl -sSLo kubernetes-server-linux-amd64.tar.gz --fail --retry 5 --retry-delay 10 --retry-all-errors https://dl.k8s.io/ci/fast//v1.36.0-alpha.2.513+93eed79b22aa09/kubernetes-server-linux-amd64.tar.gz

See #36535 for more details on the trailing slash failure.

[nrb]

/cc @damdo

[damdo]

/lgtm

/assign @upodroid

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nrb, upodroid

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• config/jobs/kubernetes/sig-cloud-provider/OWNERS [upodroid]

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[k8s-ci-robot]

@nrb: Updated the job-config configmap in namespace default at cluster test-infra-trusted using the following files:

• key ec2-e2e.yaml using file config/jobs/kubernetes/sig-cloud-provider/aws/ec2-e2e.yaml
• key periodic-e2e.yaml using file config/jobs/kubernetes/sig-cloud-provider/periodic-e2e.yaml

Details

In response to this:

Similar to a5a212f, which fixed a trailing slash for the cloud-provider-aws and sig-node jobs, this change ensures the kubetest2-ec2 jobs all use dl.k8s.io for their artifacts, rather than the gcsweb URL.

The --stage and --test-package-url parameters are also updated to not have a trailing slash, which results in 404s, such as in this job:
https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/kubernetes-sigs_provider-aws-test-infra/530/pull-kubernetes-e2e-ec2-cloud-provider-dual-stack-quick/2031854708028608512

That job used this command:

curl -sSLo kubernetes-server-linux-amd64.tar.gz --fail --retry 5 --retry-delay 10 --retry-all-errors https://dl.k8s.io/ci/fast//v1.36.0-alpha.2.513+93eed79b22aa09/kubernetes-server-linux-amd64.tar.gz

See #36535 for more details on the trailing slash failure.

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