Use broadcast_address for seeds in external seeds E2E

[rzetelskik]

Description of your changes: This PR makes the e2e test covering manual multi-datacenter setup use broadcast_address for seeds. It also unifies the usage of framework interface in this test.

Which issue is resolved by this Pull Request: Resolves https://github.com/scylladb/scylla-operator/issues/1983

/kind feature /priority important-soon /cc

[scylla-operator-bot[bot]]

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In response to [this](https://github.com/scylladb/scylla-operator/pull/1984): > > >**Description of your changes:** >This PR makes the e2e test covering manual multi-datacenter setup use broadcast_address for seeds. It also unifies the usage of framework interface in this test. > >**Which issue is resolved by this Pull Request:** >Resolves https://github.com/scylladb/scylla-operator/issues/1983 > >/kind feature >/priority important-soon >/cc Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.

[scylla-operator-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rzetelskik, zimnx

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