storage_service: Convert token through partitioner
storage_service: Convert token through partitioner

This patch ensures we use the partitioner to convert a token to
sstring instead of casting.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <1475179683-28552-1-git-send-email-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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