release-25.3: testcluster: assign unique ClusterName#158266

pav-kv merged 2 commits intocockroachdb:release-25.3cockroachdb/cockroach:release-25.3from

pav-kv:backport25.3-157868-157995pav-kv/cockroach:backport25.3-157868-157995Copy head branch name to clipboard