test: tablets_test: Create proper schema in load balancer tests
This is in preparation for load balancer changes needed to respect per-table tablet hints and respecting per-shard tablet count goal. After those changes, load balancer consults with the replication strategy in the database, so we need to create proper schema in the database. To do that, we need proper topology for replication strategies which use RF > 1, otherwise keyspace creation will fail.
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