IGNITE-20831 Make all nodes SWIM seeds in Cluster.startAndInit()

[rpuch]

https://issues.apache.org/jira/browse/IGNITE-20831

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• Formal criteria: TC status, codestyle, mandatory documentation. Also make sure to complete the following:
  - There is a single JIRA ticket related to the pull request.
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• Design: new code conforms with the design principles of the components it is added to.
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Notes

• Apache Ignite Coding Guidelines