sstables: feed new sstable with its owner shard
sstables: feed new sstable with its owner shard

Missed opportunity to feed shard id to sstable being written when
working on 67c5c8dc6776, so when sstable is reopened after sealed,
its shard doesn't need to be recomputed by open procedure.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <20171231024529.13664-1-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla