Make sharding partitioner-specific, since different partitioners interpret
the byte content differently.
Implement it by extracting the shard from the most significant bits, which
can be used to minimize cross shard traffic for range queries, and reduces
sstable sharing.
Some of the tests in DTEST take advantage of the fact that
ByteOrderedPartitioner guarantees certain ordering of partition keys.
Signed-off-by: Paweł Dziepak <pdziepak@cloudius-systems.com>
