Before, it was equalizing per-node load (tablet count), which is wrong
in heterogeneous clusters. Nodes with fewer shards will end up with
overloaded shards.
Refs #23378Closesscylladb/scylladb#23478
* github.com:scylladb/scylladb:
tablets: Make tablet allocation equalize per-shard load
tablets: load_balancer: Fix reporting of total load per node